Search

Multiplication of primary electrons at a dielectrics/gas interface exposed to an external electric field leads to the formation of ultra-fast contracted ionisation waves called surface streamers with high local electric field in their microscopic heads. We study this phenomenon in coplanar barrier discharge in atmospheric pressure air where streamers of both polarities are generated simultaneously. The electric field strength development in the discharge is determined experimentally using time-correlated single photon counting enhanced optical emission spectroscopy with high spatiotemporal resolution. We show that very high values of the electric field of even above 1200 Td (approx. 300 kV cm(-1)) can be a physical reality for positive streamer directly at the dielectric surface. The peak value for negative streamer lies under 200 kV cm(-1). In parallel, a two-dimensional fluid model describes the rapidly changing electric field and the spatiotemporal discharge dynamics in good agreement with the experimental results. We also present the theoretical results of spatiotemporal development of electron density and of charge transfer to the dielectric surface via a collapsing sheath as the discharge structure decays within a very few nanoseconds.

The development of microdischarges and the inception dynamics of subsequent microdischarges in an electrode arrangement consisting of a metal pin and a hemispherical dielectric-covered electrode, operated in air with a small toluene admixture, is studied. The discharge is operated with sinusoidal high voltage. A gated ICCD camera and a current probe enable the recording of images and current pulses of the single microdischarges, respectively, while the spatio-temporally resolved development is measured with a multi-dimensional time-correlated single photon counting technique. The overall discharge dynamics changes significantly if a concentration of 35 ppm toluene is added to dry air. A lower high voltage amplitude than in dry air is needed for stable discharge operation. This can be explained by the lower ionization energy of toluene compared to molecular oxygen and nitrogen. The microdischarge development is the same with or without admixture, i.e. a positive (cathode directed) streamer mechanism is observed. Lower mean power is dissipated into the discharge when toluene is admixed. The main effect caused by toluene admixture is the suppression of high-energy microdischarges in case of the cathodic pin half-cycle of the sinusoidal high voltage. The influence on the inception voltage by additional ionization mechanisms and volume memory effects, the consumption of energetic electrons for toluene decomposition reactions, and the modification of the surface by plasma treatment are discussed as possible reasons.

One of the primary basic plasma parameters within transient nonequilibrium plasmas is the reduced electric field strength, roughly understood as the ratio of the electrical energy given to the charged species between two collisions. While physical probes have historically been used for electric field measurements, recent advances in high intensity lasers and sensitive detection methods have allowed for non-invasive optical electric field determination in nearly any discharge configuration with time-resolution up to the sub-nanosecond range and sub-millimeter spatial resolution. This topical review serves to highlight several non-invasive methods for in situ electric field strength determination in transient plasmas ranging from high vacuum environments to atmospheric pressure and above. We will discuss the advantages and proper implementation of (i) laser induced fluorescence dip spectroscopy for measurements in low pressure RF discharges, (ii) optical emission spectroscopy based methods for nitrogen, helium or hydrogen containing discharges, (iii) electric field induced coherent Raman scattering, and (iv) electric field induced second harmonic generation. The physical mechanism for each method will be described as well as basic implementation and highlighting recent results.

A new diagnostic tool to study dielectric barrier discharges (DBDs) at atmospheric pressure by local electrical measurements is introduced. The square ground electrode is divided into 64 square segments (3.44 mm side length) so as to measure the discharge currents and gas voltages with spatial resolutions, which allows a 2D mapping. The electrical measurement results are validated by a comparison with short exposure time photographs taken from the top view of the discharge cell. For this purpose, we changed the local discharge behavior by varying locally the gas gap and the barrier capacitance and also by using a gas flow. Then, in both situations, the breakdown voltage depends on the position, and the discharge current and gas voltage are different as well. The measurements performed for a planar DBD in nitrogen with admixed nitrous oxide gas show that even if the discharge operates in a diffuse regime, the discharge does not behave exactly homogeneously on the whole surface area. The resulting electrical parameters allow us to refine the understanding of planar DBDs. The discharge activity changes the gas composition and thus, the level of preionization in the direction of the gas flow. This influences the local breakdown voltage and thus, the discharge morphology and local power density on the surface. The use of this new electrical diagnostic tool will allow us to refine the analysis of the spatial development of the discharge. This work gives some clues to improve the spatial resolution of this tool in the future.

Discharge development and streamer propagation on a dielectric surface were investigated in nitrogen-oxygen gas mixtures at atmospheric pressure. A coaxial pin-to-pin arrangement was used to generate single surface discharges driven by positive unipolar square wave high voltages of between 7 and 9 kV at 4.3 kHz. The development of surface discharges was recorded by ICCD and streak cameras. The discharges developed on the surface using pin electrodes attached directly to the dielectric plate. The accumulation over several discharge events showed a propagation front evolving from the electrode tip, while images of single discharges showed a non-uniform and branched structure of discharge channels. The electrode polarity influenced the discharge expansion and propagation velocity. Positive polarity of the metallic electrode (rising slope of HV pulses) led to a cathode-directed streamer with higher propagation velocities (5 × 105 m/s) than for negative polarity (relative to surface charges; falling slope). The increase in the O2 content in N2 from 0.1 to 20 vol% resulted in a decrease in discharge duration and an increase in streamer velocities.

Electrical breakdown in a pulsed asymmetric dielectric barrier discharge between a glass-covered mesh electrode and a grounded metal electrode in the air at atmospheric pressure is investigated. Volume discharge forms between the metal tip and the dielectric surface and spreads over the dielectric surface. Breakdown and discharge behaviors depend on the polarity of the charged electrode covered with glass compared to the metal rod electrode. In the case of the dielectric cathode (covered mesh), volume discharge features a stronger and longer-lasting emission. Volume discharge is weaker with outstretched surface discharge developing on the opposite glass electrode sustained by the embedded mesh when the metal rod functions as a cathode. The development and spatial distribution of the surface discharge depend on the relative polarity of the dielectrics caused by the charge deposition of the preceding discharge and is independent of the polarity of the applied high voltage. The discharge emission is brighter for the metal cathode and dielectric anode than for the metal anode, with a branching discharge developing and spreading in a star-like structure along the embedded grid, while a ring-like structure was observed for the metal anode and dielectric cathode. The duty cycle influences the discharge development and properties through the effects of the gas phase and surface pre-ionization.

The conversion of carbon dioxide as one of the main greenhouse gases into carbon monoxide as a chemical feedstock is considered as so-called carbon capture usage technology. Recently it was shown, that the dissociation of carbon dioxide to carbon monoxide in Dielectric Barrier Discharges can be enhanced by the addition of nitrogen gas. Here, the development of microdischarges in CO2 and CO2/N2 gas mixtures is studied. Therefore, a single filament DBD arrangement operated under sinusoidal high-voltage is investigated by means of spectroscopic and electrical diagnostics with high spatial and temporal resolution and sensitivity. The filament development is similar as in air or other nitrogen-oxygen gas mixtures, but the gas composition influences the duration and other parameters. The higher the CO2 content the weaker the filaments and the faster the quenching of excited molecular states. The optimum power dissipation into single discharge is obtained for a CO2 content between 20 and 30 vol.%.

Climate change, environmental pollution control, and resource utilization efficiency, as well as food security, sustainable agriculture, and water supply are among the main challenges facing society today. Expertise across different academic fields, technologies, and disciplines is needed to generate new ideas to meet these challenges. This white paper aims to provide a written summary by describing the main aspects and possibilities of the technology. It shows that plasma science and technology can make significant contributions to address the mentioned issues. The paper also addresses to people in the scientific community (inside and outside plasma science) to give inspiration for further work in these fields.

The Ar( 3 P 2) metastable density in the effluent of the cold atmospheric pressure plasma jet kINPen was investigated as a function of the feed gas humidity, the gas curtain composition, and the distance from the nozzle by means of laser atomic absorption spectroscopy. The filamentary character of the plasma jet was considered as the absorption signals are from single individual events. From the effective lifetime, the quenching coefficient for Ar( 3 P 2) by water was determined. A maximum Ar( 3 P 2) density of ( 6.0 ± 0.7 ) × 10 13 cm − 3 was obtained close to the nozzle for a feed gas humidity of 20 ppm. The densities near the nozzle decreased inversely proportional to the water content in the feed gas leveling off at approximately 1 × 10 13 cm − 3, independently from the gas curtain composition. With the addition of water to the feed gas, the excitation dynamics changed, and the production and lifetime of Ar( 3 P 2) was reduced. The impact of Ar( 3 P 2) on the reactive species composition in the effluent was found to be smaller than within the plasma zone inside the plasma jet device.

A dielectric barrier discharge over distilled water was investigated by means of synchronized, fast electrical and optical diagnostics. For this purpose, a single, alumina-covered electrode was placed above a water surface and a grounded tungsten electrode underwater, while the gas gap was constantly flushed with synthetic air at atmospheric pressure. Discharge events occur at rising and falling slopes or at the plateaus of the applied high-voltage pulse. Due to the synchronized diagnostics, a direct comparison of electrical characteristics and optical features of individual discharge events was performed. In most cases, a single discharge channel develops between the tips of the dielectric and the Taylor cone. Surface discharge channels can also occur in the upper part of the electrodes, which can be explained by a water layer being formed on the dielectric and acting as a virtual electrode. The discharge morphology and dynamics were found to be independent of the voltage polarity, which contradicts to known experiments with bare metal pin electrodes instead of dielectric-covered ones.

Dielectric barrier discharges (DBDs) are characterized by electrical measurements interpreted on the basis of equivalent circuits. The concept of the simplest equivalent circuit of volume DBDs is expanded to surface DBDs (SDBDs); this was completed by taking into account the discharge expansion on the dielectric-gas interface. It is assumed, that this expansion is not limited by the dimension of the electrodes. This approach delivers an analytical relationship for the dissipated power as a function of the applied voltage amplitude. It applies to SDBDs with sufficiently long embedded electrodes and operated by sinusoidal high voltages. The obtained relations were validated by comparison with experimental data obtained from previous work devoted to SDBDs with 20 mm elongated electrodes operated in ambient air and for applied peak-to-peak voltages of up to 20 kV at 1 kHz frequency. The dependencies derived from the equivalent circuit agree well with experimentally recorded charge and dissipated energy.

The emissions of airborne contaminants from various industrial processes are an important source of air pollution and presents problems for human health and the environment in general. The removal of gaseous pollutants, such of nitrogen and sulphur oxides (NOx and SOx), from exhaust gases, or volatile organic compounds (VOC) emitted from various industrial processes is of continuous challenge in the environmental engineering. Plasma-based pollutant decomposition methods emerge as promising techniques, but little is known about their overall environmental performance. We compared two plasma based technologies (Electron Beam Flue Gas Treatment (EBFGT) and Dielectric Barrier Discharge (DBD) against the conventional methods (Wet Flue Gas Desulphurization with Selective Catalytic Reduction, WFGD+SCR, biofiltration and adsorption) using life cycle analysis (LCA), which took into account the usage of materials, waste generation and energy consumption. Five main categories (Global Warming, Ozone Layer Depletion, Acidification, Euthrophication and Human Toxicity, based on the CML2001 method) were used for the environmental impact evaluation. Based on CML2001 IKP Experts weighting, WFGD+SCR technology is marginally more environmentally friendly in comparison to EBFGT (59.25 to 73.74 CML2001 IKP Experts score). The generation of byproducts (in this case gypsum waste) is the main disadvantage of the WFGD+SCR. At the same time, EBFGT enables formation of useful byproducts, which are suitable to be utilized as fertilizers in the agriculture sector. On the other hand, DBD was six times more favorable to the environment than the adsorbtion and more than two times more environmentally friendly than the biofiltration technology (4.23, 27.78 and 9.29 relative units, respectively). With respect to the adsorption/thermal incineration of VOCs, both the electricity and the material consumption, as well as the management of byproducts caused the highest impact. In case of biofiltration, the management of remaining filter material waste (in this case, landfilling) was the most significant. Relatively high electrical energy demand causes lower positioning of plasma based technologies in cases where no other materials are utilized and major waste is formed. In turn, many traditional end-of pipe technologies are associated with high amounts of process waste, which provides plasma technologies with an opportunity to establish them in the market as more efficient and in many occasions, more environment-friendly ones.

Fuel and synthesis gases generated by thermochemical gasification of renewable biomass resources and organic waste fractions are considered to be promising for recent and future energy demands. However, the presence of tar species in the gas mixture is an economic obstacle in the commercialization of this technology. The influence of non-thermal plasma on gas phase naphthalene which served as tar model compound, in the presence of solids was examined. The naphthalene was evaporated into a N2/H2/CO/CO2 gas atmosphere and led through a packed-bed, atmospheric plasma reactor operated at a temperature of 350 °C. The influence of two bed materials - glass beads and glass beads mixed with char particles - was studied. The char particles originated from real gasification processes with woody biomass as feedstock. With both reactor fillings, the content of naphthalene in the gas phase was reduced. The characteristic energy β of the naphthalene removal was found to be βno char = 952 ± 77 Jl–1 and βwith char = 232 ± 10 Jl–1, respectively. Consequently, the addition of char material leads to a naphthalene removal efficiency increased by a factor of about four. Furthermore the formation of ammonia (NH3), a by-product of the plasma reactions, was suppressed in the presence of char. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface dielectric barrier discharges are investigated in order to explore the combined effects of barrier thickness and microstructure of the exposed electrode on the ion wind generation. Actuators with straight and structured high voltage electrodes with characteristic sizes of 200 and 250 µm and dielectric thicknesses of 0.5, 1 and 2 mm are compared. It is observed that: i) actuator efficiency of ion wind generation strongly depends on the applied voltage amplitude; ii) operation voltage depends on the dielectric thickness logarithmically; iii) electrode microstructure slightly increases the dynamic pressure (few percent in maximum), however the effect decreases with thicker dielectrics and smaller electrode structures; iv) the pattern of the most intensive discharge parts as well as the dielectric erosion repeats the regular structure of the electrodes down to 200 µm. Several identical samples are tested during different days to estimate the impact of the air humidity and the degradation of the dielectric. The microscale precision of the sample manufacture was accomplished by a commercial facility for printed circuit boards.

The nature and physical parameters of dielectric barrier discharges (DBDs) are determined by the presence of dielectric material in the discharge gap. The charging of the dielectric barrier is responsible for the non-thermal regime as it limits the local energy dissipation. In an operating DBD residual surface charges can influence the distribution and development of the plasma in the following discharge cycles1. In order to learn more about residual surface charge role an experiment with a rotating dielectric electrode and a pin electrode (325 μm tip radius) is realized2. The rotating dielectric barrier enables DBD-operation with DC high voltage and, the remaining surface charges are removed by a second grounded electrode which is sliding over the dielectric. Thus, single, repetitive microdischarges in air at atmospheric pressure are ignited without participation of residual surface charges. These microdischarges were investigated by ICCD camera, electrical measurements and time-correlated single photon counting (sub-ns, sub-mm and spectral resolution). For positive polarity of the pin electrode a positive streamer starting from the middle of the gap followed by a secondary wave starting from the metal electrode is observed. For negative polarity an anode directed wave of light and a weaker glow in front of the cathode are obtained.

The phenomenology and breakdown mechanism of dielectric barrier discharges are strongly determined by volume and surface memory effects. In particular, the pre-ionization provided by residual species in the volume or surface charges on the dielectrics influences the breakdown behavior of filamentary and diffuse discharges. This was investigated by advanced diagnostics such as streak camera imaging, laser photodetachment of negative ions and laser photodesorption of electrons from dielectric surfaces in correlation with 1D fluid modeling. The streak camera images show that an increasing number of residual charges in the volume changes the microdischarge breakdown in air-like gas mixtures from a cathode-directed streamer to a simultaneous propagation of cathode- and anode-directed streamers. In contrast, seed electrons are important for the pre-ionization if the density of residual charges in the volume is low. One source of seed electrons are negative ions, whose density exceeds the electron density during the pre-phase of diffuse helium–oxygen barrier discharges as indicated by the laser photodetachment experiments. Electrons desorbed from the cathodic dielectric have an even larger influence. They induce a transition from the glow-like to the Townsend-like discharge mode in nominally pure helium. Apart from analyzing the importance of the pre-ionization for the breakdown mechanism, the opportunities for manipulating the lateral structure and discharge modes are discussed. For this purpose, the intensity and diameter of a diffuse discharge in helium are controlled by an illuminated semiconducting barrier.

Bedingt durch seine Eigenschaften laufen in physikalischen Plasmen komplexe chemische Prozesse ab, an denen auch Elektronen mit einer hohen mittleren Energie beteiligt sein konnen. Physikalische Plasmen sind Vielteilchensysteme in Form fluider oder gasartiger Mischungen freier Elektronen und Ionen sowie neutraler Teilchen und Photonen. Die chemischen Stoffumwandlungen einschlieslich der Prozesse im Volumen und an den Plasmagrenzflachen sind unter dem Begriff der Plasmachemie zusammengefasst. Generell ist zwischen thermischen und nichtthermischen Plasmen zu unterscheiden. In thermischen Plasmen liegt ein thermisches Gleichgewicht aller Einzelkomponenten mit- und untereinander vor und es gilt das Massenwirkungsgesetz. In nichtthermischen Plasmen liegt ein thermodynamisches Nicht-Gleichgewicht zwischen Elektronen einerseits und den Ionen und Neutralteilchen andererseits vor. Die mittlere Energie der Elektronen kann die der Neutralteilchen und Ionen um bis zu drei Grosenordnungen ubertreffen, wobei letztere nahe Raumtemperatur vorliegen konnen. Die Plasmachemie ist bis heute ein interessantes Forschungsfeld und Plasmareaktoren besitzen eine hohe technologische Relevanz. An den Beispielen der Acetylensynthese (thermisches Lichtbogenplasma, Plasmapyrolyse) und der Ozongeneration (nichtthermische Barrierenentladung) werden exemplarisch beiden Zweige der Plasmachemie dargestellt und Reaktorkonfigurationen erlautert.

The continuous development of novel plasma sources for therapeutic applications is leading to a growing demand for test protocols that allow a standardized physical characterization and the estimation of biological efficacy. These data are mandatory for estimating the biological performance of a given plasma source, and to serve as a tool that enables a rough comparison of different plasma sources. Additionally, data can be used for the technical improvement of plasma devices, and regarded as a preliminary stage for the licensing of such sources as medical devices. Thus, a DIN SPEC 91315:2014-06 was implemented to characterize plasma sources in terms of their biological performance including risk and safety potential for the therapeutic use of plasma in medicine.

The decomposition of various volatile organic compounds (VOCs), namely butyl acetate, styrene, and methanol, by means of non-thermal plasma technology was investigated in different industrial exhaust gases. Although a great deal of effort on the investigation of these VOCs can be found in literature, data regarding the application in real exhaust gases are missing and provided in this contribution. Measurements were performed in an oil shale processing plant in Estonia and in a yacht hall production site in Poland. Up to 71 % of butyl acetate at a specific input energy (SIE) of about 220 J/L and more than 74 % of styrene and methanol at SIE > 300 J/L were decomposed. The energy efficiency of the decomposition processes was analyzed as well as the products formed by the plasma process. Energy constants of k E

Direct and indirect plasma oxidation of NO x was tested in a medium-scale test-bench at gas flows of 50 slm (3 m 3 /h). For direct plasma oxidation the synthetic flue gas was directed through a stacked DBD reactor. For indirect plasma oxidation, a DBD reactor was used to generate ozone from pure O 2 and the plasma treated gas including ozone was mixed with flue gas at the entrance of a 6 m long serpentine-like reaction chamber which allowed reaction times longer than 10 s. At relatively low NO x concentrations of 200 ppm, both oxidation methods gave similar results. However, the temperature increase of the DBD reactor decreased the long-term efficiency of direct plasma oxidation. At the same time, the efficiency of indirect oxidation increased at elevated reactor temperatures. Additional experiments were carried out to investigate the improvement of indirect oxidation by the introduction of catalyst to the reaction zone. Small-scale experiments with TiO 2 powder demonstrated considerable efficiency gain for NO x oxidation while in medium-scale experiments, the efficiency improvement remained negligible.

Unsteady loading rates can affect the proper operation of a biofilter. In addition, biofiltration is known to be less effective when dealing with poorly soluble substances, like some volatile organic compounds (VOCs). A non-thermal plasma (NTP) produced with a dielectric barrier discharge (DBD) was studied as an option to pre-treat an air stream contaminated by a mixture of VOCs. Therefore, the plasma reactor was operated upstream of a laboratory-scale biofilter. Air admixed with toluene, n -heptane, p -xylene, ethylbenzene and benzene with average concentrations of 95.6, 49.4, 60.8, 47.3 and 36.6 ppm, respectively, was used as a model polluted gas, as these contaminants represent the air stripped by an oil-refinery wastewater treatment plant. Peaks of loading rates at the inlet of the biofilter were simulated by the increase of the flow rates of VOCs. The operation of NTP, with specific energy densities between 92 J L −1 and 256 J L −1 allowed reducing the VOC concentrations down to the level of optimal biofilter operation. In addition, non-water soluble VOCs were converted to more soluble compounds by the plasma treatment. In this first attempt to investigate the synergies between NTP and biofiltration, NTP reveals as a promising option to pre-treat effluents upstream of biofilters for optimized operation.

Dielectric barrier discharges (DBDs) are plasmas generated in configurations with an insulating (dielectric) material between the electrodes which is responsible for a self-pulsing operation. DBDs are a typical example of nonthermal atmospheric or normal pressure gas discharges. Initially used for the generation of ozone, they have opened up many other fields of application. Therefore DBDs are a relevant tool in current plasma technology as well as an object for fundamental studies. Another motivation for further research is the fact that so-called partial discharges in insulated high voltage systems are special types of DBDs. The breakdown processes, the formation of structures, and the role of surface processes are currently under investigation. This review is intended to give an update to the already existing literature on DBDs considering the research and development within the last two decades. The main principles and different modes of discharge generation are summarized. A collection of known as well as special electrode configurations and reactor designs will be presented. This shall demonstrate the different and broad possibilities, but also the similarities and common aspects of devices for different fields of applications explored within the last years. The main part is devoted to the progress on the investigation of different aspects of breakdown and plasma formation with the focus on single filaments or microdischarges. This includes a summary of the current knowledge on the electrical characterization of filamentary DBDs. In particular, the recent new insights on the elementary volume and surface memory mechanisms in these discharges will be discussed. An outlook for the forthcoming challenges on research and development will be given.

Various solid Cu-containing catalysts were prepared. Their performance in the selective catalytic reduction of NOx using propene as reducing agent from 150 to 450 °C in an O2-rich model exhaust gas in the presence of water vapor was investigated. This research aimed at the development of a catalytic NOx to N2 (DeNOx) step to be part of a ship diesel exhaust abatement system in combination with other techniques, such as nonthermal plasma. Among the catalysts tested, Cu on zeolite Y with an optimized load of 16 wt % (denoted as 16Cu/Y) displayed excellent DeNOx activity with highest selectivity toward N2 at 290 °C. The influence of other variables, such as Cu load, calcination temperature, feed composition, and GHSV on the performance of 16Cu/Y was studied, as well. The highest N2 yield of 98% was achieved using 2000 ppm of propene in the gas feed. The presence of O2 proved to be a crucial factor for promoting the selective reduction of NOx with C3H6 over this catalyst. On the other hand, the presence of wa...

The status of the research into and the application of non-thermal plasmas for the pollutant degradation in gases is discussed, including some fundamental topics and engineering issues. Two reactor concepts, both based on dielectric barrier discharges (DBDs), are presented and investigated for various tasks. The DBD-stack reactor shows a very good scalability and was investigated for the oxidation of NO in combustion gases (shipping diesel engine exhausts). The oxidation processes were significantly enhanced by the admixture of hydrocarbons. Significant NO conversion at low specific energy densities below 100 J/L were achieved in laboratory and test bench studies. The water falling film reactor demonstrated its feasibility for the removal of hydrocarbon pollutants from gases. Undecane, a long-chain, harmful hydrocarbon, was decomposed. The conversion of non-soluble compounds into soluble ones (formic acid) is a promising development towards a compact plasma-assisted scrubbing technology. These approaches are good progress not only in the field of environmental plasma application, but also for indoor air quality, hygiene, and plasma synthesis. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A molecular beam mass spectrometer has been calibrated and used to measure the air entrainment, nitric oxide and ozone concentrations in the effluent of a cold atmospheric pressure argon RF driven plasma jet. The approaches for calibrating the mass spectrometer for different species are described in detail. Gas phase densities of ozone and nitric oxide up to 7.5 ppm and 4 ppm, respectively, have been measured in the far effluent of the argon plasma jet. The difference in air entrainment when the plasma is undisturbed or is close to a well, which is the case for e.g. in vitro plasma–cell interaction studies, is shown. In addition, an exponential decay of the positive ion flux as a function of distance in the effluent is obtained. Furthermore, the effect of plasma power, duty cycle and air and O2 admixtures introduced into the argon flow on the NO and O3 production is presented, including the possibility of independent control of the NO and O3 flux from the jet.

Effects of plasma assisted waste air treatment from a water treatment plant have been investigated in several field tests. In particular the off-air for a thermal sludge dryer was investigated and treated. The intention of this study was to proof whether plasma assisted technologies are a possible solution for the removal of odour from waster air emitted by wastewater treatment facilities. The plasma treatment was combined with a catalytic (cupper-manganese) unit, a scrubbing unit, or a bio filter in order to demonstrate the abilities for waste air deodorization. The inlet and outlet gas was analysed by means of FTIR, FID, and chemical sensors and the odour removal was investigated by standardized olfactometry. A significant reduction of hydrogen sulphide and methane by means of combined plasma-catalyst-treatment has been measured, but the removal of hydrogen sulphide leads to the formation of unwanted by-products. Main effects of plasma treatment in the field tests can be compared to the results of laboratory studies published in the literature. A significant odour reduction up to about 90% was measured. Aldehydes and other hydrocarbons are marginally removed by plasma treatment as well as by the bio filter. The bio filter released sulphur containing substances (DMS, CS2, DMDS) which can be destroyed by plasma-catalytic treatment. Based on the results of the field tests a reliable concept for an industrial after treatment installation has been designed as described. Due to the high content of H2S a scrubber as the first treatment unit is desired. Downstream the scrubber the plasma/catalytic unit combined with the existing bio filter is proposed for the removal of the hydrocarbons and other odorous constituents.

We investigate single microdischarges (MDs) in a sinusoidally operated barrier corona discharge in air. For the voltage amplitude being applied, two subsequent MDs appear in the anodic pin half-cycle. The developments of these subsequent MDs were studied and presented in detail in a previous contribution [Jahanbakhsh et al., Plasma Sources Sci. Technol. 27, 115011 (2018)]. In the present study, the reduced electric field strength ( E / n) values of the MDs are determined. In addition, the current pulses are synchronized, with a subnanosecond time resolution, to the spatiotemporally resolved light emission and E / n development of the MDs. It is proposed that the current pulse derivative maximum corresponds to the streamer head arrival on the cathode surface. Therefore, the derivatives of the current pulses are used to synchronize the light emission and current measurements. Based on this synchronization, spatiotemporally resolved light emissions at different positions are compared to the averaged current pulses. Considering the observed correlations, it is proposed that after the arrival of the streamer head on the dielectric (cathode) surface and bulk plasma formation, the ionization processes near the dielectric surface are the dominant source of electron current production. The determination of the E / n is based on the analysis of the time-correlated single photon counting results for the molecular states of the first negative and the second positive systems of nitrogen. The E / n increases during the streamer propagation in the gap, reaching its maximum value at the impact of the streamer on the cathode. The E / n values for the second group MDs are lower only in the vicinity of the dielectric surface, which can be attributed to the positive residual surface charges from the first group MDs.

Measurements of current and voltage are the basic diagnostics for electrical discharges. However, in the case of dielectric barrier discharges (DBDs), the measured current and voltage waveforms are influenced by the discharge reactor geometry, and thus, interpretation of measured quantities is required to determine the discharge properties. This contribution presents the main stages of the development of electrical diagnostics of DBDs, which are based on lumped electrical elements. The compilation and revision of the contributions to the equivalent circuit approach are targeted to indicate: (1) the interconnection between the stage of development, (2) its applicability, and (3) the current state-of-the-art of this approach.

Atmospheric non-thermal plasma has been recognized as a successful tool for the treatment of exhaust and waste air for abatement of pollutants, air cleaning, and odor removal. To improve the efficiency of plasma cleaning processes a combination of plasma with adsorption filters and or catalysts is used. The fundamental interaction mechanisms of the surface, plasma, and gas remain the subject of further investigations of the details. A quantitative FTIR-spectroscopic study of the effect of surface barrier discharge on the adsorption and desorption of ethanol at activated carbon is presented. First of all the adsorption and desorption were characterized for different input concentrations and different carrier gas flows without operating the plasma. After that the interaction of the plasma and the gas mixture was analyzed. Finally the activated carbon filter was reinstalled behind the plasma stage and the loading and unloading of the activated carbon filter element were investigated while burning the plasma. It is shown that the plasma stage initiates an additional decomposition of ethanol at the surface of the activated carbon because of the interaction of long-lived O3 with physical adsorbed C2H5OH. The total amount of filtered C2H5OH does not change but the portion of decomposed C2H5OH that is not rinsed out increases. The plasma caused effect at the surface reaches 68% of the effect of plasma in the gas phase.

A dielectric barrier discharge (DBD) of coaxial geometry has been investigated. The discharge cell was filled by 100 mbar of argon and driven by positive square voltage pulses with a rise time of 20 ns and 75 ns. The internal discharge characteristics such as the discharge current, the gas gap voltage, the instantaneous power and energy have been determined from measured current and voltage waveforms. The peculiarities of the experimental evaluation of the discharge parameters are discussed in detail. Special attention is paid to the accurate experimental determination of the key capacitance values of the DBD, namely the capacitance of the reactor cell Ccell and the capacitance of the dielectric barriers Cd. The influence of the capacitance value accuracy on precision of electrical characterization is demonstrated and it is shown that a small uncertainty in the Cd value leads to large errors in the evaluation of the gas gap voltage. Nevertheless, the obtained accuracy of the capacitance values allows the reliable comparison of the electrical DBD parameters. These are sensitive to the mode of discharge excitation. The shortening of the voltage rise time leads to the increase of the total and instantaneous energy as well as the peak power dissipated into the discharge. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A radio-frequency atmospheric pressure argon plasma jet is used for the inactivation of bacteria (Pseudomonas aeruginosa) in solutions. The source is characterized by measurements of power dissipation, gas temperature, absolute UV irradiance as well as mass spectrometry measurements of emitted ions. The plasma-induced liquid chemistry is studied by performing liquid ion chromatography and hydrogen peroxide concentration measurements on treated distilled water samples. Additionally, a quantitative estimation of an extensive liquid chemistry induced by the plasma is made by solution kinetics calculations. The role of the different active components of the plasma is evaluated based on either measurements, as mentioned above, or estimations based on published data of measurements of those components. For the experimental conditions being considered in this work, it is shown that the bactericidal effect can be solely ascribed to plasma-induced liquid chemistry, leading to the production of stable and transient chemical species. It is shown that HNO2, ONOO − and H2O2 are present in the liquid phase in similar quantities to concentrations which are reported in the literature to cause bacterial inactivation. The importance of plasma-induced chemistry at the gas‐liquid interface is illustrated and discussed in detail. (Some figures may appear in colour only in the online journal)

The NO oxidation performance in a non-thermal plasma (NTP) reactor under realistic synthetic exhaust gas compositions is investigated. The gas compositions differ mainly in the NO–NO2 ratio and represent different modes of operation of a marine diesel engine. It is found that the maximum NO oxidation efficiency is independent on the NO–NO2 ratio. Up to 55 % of the NO is mainly oxidised to NO2 in all gas mixtures being analysed. However, the specific energy density needed to reach the highest NO oxidation varies with the gas composition between 15 and 60 J/L. The performance of the NTP-reactor was significantly improved by the addition of propene (C3H6) acting as an additional oxidising agent. The energy consumption for NO–NO2 conversion was found to be between 20 and 45 eV/NO, depending on the ratio of the added propene as well as the initial concentrations of nitrogen oxides.

A two-dimensional array of micro-discharges in air at atmospheric pressure is studied by cross correlation spectroscopy (CCS) [1]. The array consists of two insulated metal meshes and the discharge is generated by AC voltages at 20 kHz. A gas flow is applied through the array. The temporal resolution of CCS in the sub-ns range allowed to investigate the micro-discharges dynamics within a single micro-discharge hole end-on.

The research and development of plasma sources, which can be used for therapeutic applications in the new and emerging field of plasma medicine, has gained more and more interest during recent years. These applications require cold nonthermal plasmas operating at atmospheric pressure. Due to the fact that, in general, plasma on or in the human body is a challenge both for medicine and plasma physics, basic research combining experimental physical and biological investigation and modeling is necessary to provide the required knowledge for therapeutic applications. It turned out that each application needs a special tailor-made plasma source, passing a minimum set of physical and biological tests before it can be considered for medical use. In addition to atmospheric-pressure plasma jets, dielectric barrier discharges offer great potential for a variety of medical indications. A new 2-D and even 3-D acting plasma source is introduced, exemplified for a possible decontamination of human extremities or similar tasks. In contradiction to most of today's existing plasma sources with fixed electrodes and nozzles, the prototype uses flexible electrodes to automatically adapt the plasma under equal and stable conditions to nearly all surface structures. First, physical and biological investigations demonstrate the general potential for therapeutic applications on preferably intact skin surfaces.

A discharge cell configuration combining three high-end diagnostic techniques (cross-correlation spectroscopy, electro-optic Pockels effect and laser induced fluorescence spectroscopy) has been developed. The joint application of these diagnostics enables the investigation of surface and bulk processes in barrier discharges in different arrangements. Surface charge density, N2(A) metastable state density, and optical radiation of plasma as three key parameters can be measured and correlated under identical and well-defined experimental conditions. Systematic measurements of absolute surface charge densities and nitrogen metastable concentrations are presented for different operation modes. The operation mode is mainly controlled by the gas composition, the discharge cell geometry, and the properties of the applied voltage. In particular, in pure helium the unusual Townsend-like discharge was investigated in detail. The described arrangements and the knowledge about reproducible control of discharge modes are an excellent base for the systematic investigation of the interaction between plasma and dielectric surface and its role on the formation, development, and structure of barrier discharges (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Summary Background Over the past few years, plasma medicine has become an important field in medical science. Cold plasma has proven anti-inflammatory, antimicrobial and antineoplastic effects. Aim To test the decontamination power of two cold plasma sources [low-temperature atmospheric pressure plasma jet (APPJ) and dielectric barrier discharge plasma (DBD)] in vivo on human fingertips. Methods After 3, 15, 30, 60, 90, 120, 150, 180, 210 and 240 s of spot treatment with the APPJ and DBD, the log reduction factors (RFs) of physiological (PF) and artificially (AF) contaminated flora ( Staphylococcus epidermidis and Micrococcus luteus ) were calculated. The bacterial load was determined after counting. Tolerance (paresthesia, pain and heat) was measured using a numerical rating scale. Findings Both plasma devices led to a significant reduction in PF and AF. The maximum log reduction factors for PF were 1.3 for the DBD at 210 s and 0.8 for the APPJ at 60 s. For AF, the maximum log reduction factors were 1.7 for the DBD at 90 s and 1.4 for the APPJ at 120 s. Treatment with both devices was well tolerated. Conclusion Both the APPJ and DBD were highly effective in eradicating PF and AF from the fingertips of healthy volunteers. No plasma-resistant isolates were observed. Cold plasma appears to have potential for skin disinfection. For hand hygiene purposes, plasma exposure times would need to be reduced significantly by technical means.

Summary Background: Cold plasma, a new treatment principle in dermatology based on ionic discharge delivering reactive molecular species and UV-light, exhibits strong antimicrobial efficacy in vitro and in vivo. Before implementing plasma as new medical treatment tool, its safety must be proven, as well as assessing skin tolerance and patient acceptance. Patients and Methods: We investigated the plasma effects of three different plasma sources (pulsed, non-pulsed atmospheric pressure plasma jet (APPJ) and a dielectric barrier discharge (DBD)) on the transepidermal water loss (TEWL) and skin moisture after treating the fingertips of four healthy male volunteers. Results: TEWL values were reduced by pulsed APPJ and DBD by about 20% but increased after non-pulsed APPJ by 5–20%. TEWL values normalized 30 min after all forms of plasma treatment. Skin moisture was increased immediately and 30 min after treatment with pulsed APPJ but was not affected by non-pulsed APPJ and DBD. Conclusions: All plasma treatments were well-tolerated and did not damage the skin barrier nor cause skin dryness. Cold plasma fulfils basic recommendations for safe use on human skin and as future option may serve as the first physical skin antiseptic.

Treatment of aqueous liquids by surface-DBD in atmospheric air resulted in bactericidal activity of the liquid itself. A 7 min treatment of sodium chloride (NaCl) solution and its immediate addition to Escherichia coli resulted in a complete bacteria inactivation (≥7 log) after 15 min exposure time. With a 30 min delay between plasma treatment of liquid and its addition to the bacteria, bactericidal effect was reduced but still detectable. Nitrate (), nitrite (), and hydrogen peroxide (H2O2), respectively, as well as strong acidification are detected in plasma treated liquids and can explain this bactericidal activity partially. Combination of 1.5 mg · L−1 and 2.5 mg · L−1 H2O2 at pH 3 results in maximum 3.5 log E. coli reduction within 60 min. Plasma diagnostics and liquid analytics are combined with theoretical considerations to focus possible reaction channels of plasma–water interactions. Using FT-IR, stable molecules like nitrous oxide (N2O), ozone (O3), carbon dioxide (CO2), and traces of nitric acid (HNO3) and/or peroxynitrous acid (ONOOH) were measured. Reactions of these molecules from the plasma/gas phase with the aqueous liquid can result in acidification and generation of H2O2, , and or peroxynitrite (ONOO−), respectively, via reactions which are associated with the occurrence of several more or less stable but biologically active chemical intermediates like or nitrogen dioxide (). On the other hand, H2O2, , and /ONOO− could serve as starting reaction partners to generate , , , or hydroxyl radicals () in the liquid.