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Plasma medicine is an expanding focus and offers new aspects of therapy combining potent physical partial efficacies, like such as ultraviolet, infrared, and reactive species and particles, and nowadays, many successful treatments of different illnesses have been described. Fungal skin and nail infections pose significant therapeutic and economical problems. To test the plasma susceptibility of clinical strains of the most frequently encountered fungal species involved in dermatomycosis, clinical isolates of Trichophyton interdigitale, Trichophyton rubrum, Microsporum canis, and Candida albicans were irradiated by a cold atmospheric pressure plasma jet. Punctual plasma irradiation eradicated fungal growth of all species with the largest inactivation zones with most progress in the first 15 s of treatment, treating C. albicans and least progress in that of , the lowest being M. canis. No isolate exhibited resistance to plasma treatment. Plasma treatment also completely eradicated reproductive fungal elements of T. interdigitale in dandruff of patients with tinea pedis ex vivo and in the environment in contaminated shoes. Accordingly, cold plasma seems suited to antifungal in vivo treatment of fungal skin infections and decontamination of environmental infective material.

The spatio-temporal development of single microdischarges in an asymmetric surface barrier discharge arrangement was investigated. The arrangement consisted of two needle electrodes laid on a dielectric plate. The discharge was operated in dry air at atmospheric pressure with a sinusoidal applied voltage. The discharge was investigated by current-voltage measurements as well as two optical techniques, the intensified CCD imaging (equipped with a far-field microscope) and the cross-correlation spectroscopy. While the combined methods of iCCD imaging and far-field microscope recorded two-dimensional pictures with a high spatial resolution, the CCS recorded the spatio-temporal development of the luminosity of the 0–0 transitions of the second positive system (λ = 337.1 nm) and first negative system (λ = 391.5 nm) of molecular nitrogen. The intensities of these two bands were measured with a fine spatial and temporal resolution. It was found that both half periods have significant differences in the mechanism. While the positive half period behaves similar as volume or coplanar barrier discharges, during the negative half period no positive streamer was detected.

Plasma-based treatment of chronic wounds or skin diseases as well as tissue engineering or tumor treatment is an extremely promising field. First practical studies are promising, and plasma medicine as an independent medical field is emerging worldwide. While during the last years the basics of sterilizing effects of plasmas were well studied, concepts of tailor-made plasma sources which meet the technical requirements of medical instrumentation are still less developed. Indeed, studies on the verification of selective antiseptic effects of plasmas are required, but the development of advanced plasma sources for biomedical applications and a profound knowledge of their physics, chemistry, and parameters must be contributed by physical research. Considering atmospheric-pressure plasma sources, the determination of discharge development and plasma parameters is a great challenge, due to the high complexity and limited diagnostic approaches. This contribution gives an overview on plasma sources for therapeutic applications in plasma medicine. Selected specific plasma sources that are used for the investigation of various biological effects are presented and discussed. Furthermore, the needs, prospects, and approaches for its characterization from the fundamental plasma physical point of view will be discussed.

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.

Die Reduzierung der Schadstoffemission aus Abgasen und Abluft wird mehr und mehr zu einer existenziellen Aufgabe in der hochentwickelten Industriegesellschaft. In Folge der Wirkung auf die Luft, den Boden und die Gewasser beeinflussen Verunreinigungen die gesamte Umwelt und damit die menschliche Gesundheit. Aus diesem Grund unterliegen Umweltnormen und –standards einer standigen Verscharfung seitens nationaler und internationaler Behorden. Moglichkeiten zur Eindammung der Luftverschmutzung mit Hilfe von nichtthermischen Plasmen sind bereits gut bekannt. Plasmen enthalten aktive und auserst reaktive Komponenten wie Elektronen, Ionen, Atome, Molekule und Radikale, die Schadstoffmolekule und Aerosole abbauen konnen. Der vorliegende Beitrag gibt einen Uberblick zu den Moglichkeiten der Schadstoffbeseitigung mittels nichtthermischer Plasmen. Kommerziell verfugbare und nahezu kommerzialisierte plasmabasierende und plasmaunterstutzte Prozesse zur Abgasbehandlung und Geruchsbeseitigung werden vorgestellt. Die gegenwartigen Trends und Konzepte werden diskutiert. Non-thermal plasma for emission protection: State of the art and future prospects The reduction of emissions from exhaust gas streams is becoming more and more important issue in the highly industrialised society. Due to its impact on air, soil and water exhaust pollutions affect the whole environment and thus human health. Therefore environmental norms and standards are constantly increased by national and international authorities. The possibilities of air-pollution control by means of non-thermal plasmas are well known. Plasmas contain active and highly reactive species, in particular electrons, ions, atoms, molecules, and radicals, which can decompose of filter pollutant molecules and particulate matter. This contribution intends to summarize the possibilities or pollution control by means of non-thermal plasmas. Commercially available plasma based and plasma assisted processes for flue gas treatment and deodorization are described. Current trends and concepts will be discussed.

Water disinfection by indirect plasma treatment was investigated using a surface dielectric barrier discharge (DBD). Liquid was neither part of the discharge electrode configuration nor stirred during plasma treatment. High concentrations (106–108 cfu·mL−1) of Escherichia coli and Staphylococcus aureus have been completely inactivated within 5–15 min, depending on liquid sample volume. Inactivation occurred in non-buffered liquids, only, where pH decrease was found. Measurements of pH, nitrate, and nitrite concentrations after DBD plasma or NO gas treatment lead to the conclusion that nitric acid formation from plasma-generated reactive nitrogen species are the main source of liquid acidification. Incubation of bacteria in nitric acid alone did not result in comparable inactivation effects. Increase of H2O2 concentration was found as a result of plasma treatment of liquids but not after treatment by NO gas. Therefore, synergistic action of both reactive oxygen and nitrogen species are discussed to be responsible for antimicrobial plasma effects.

A set of minimum standards which have to be adjusted if a plasma source is intended for therapeutic applications has been defined. The main performance parameters of an optimized low-temperature atmospheric pressure plasma source were investigated and controlled. This has been done to discuss global risk factors that have to be avoided during application. By using this minimum standard set of parameters it should become possible to directly compare different atmospheric plasma sources for special biomedical applications and to derive optimum treatment parameters found on different sources and locations. Up to now a strict comparison is mainly done indirectly by investigating the effect of the plasma treatment on the surface. Temperature, thermal load, UV radiation, production of radicals and toxic gases and the resulting biological effects have been investigated to minimize risk factors and to indicate first meaningful parameter ranges (dosages) for therapeutic applications. The mix of these parameters (like mixing a cocktail) has to be adapted individually for each application. For practical use constant energetic conditions at the visible tip of the investigated jet could be observed, therefore it could be recommended to adjust the visible tip of the pen in such a way that it just touches the surface.

Radio-frequency-driven plasma jets in argon at atmospheric pressure have been shown to emit a significant amount of UV and VUV radiation. There is an increasing interest in the use of UV and VUV photons in many fields of research and in industry, in particular for life-science applications. In order to study the antimicrobial effect of plasma-emitted UV and VUV radiation, microbiological tests and plasma diagnostics are combined. In particular, quantitative values of irradiance are estimated. The VUV emission of the plasma jet is dominated by the emission of argon excimer (Ar2). The recorded spectra between 115 and 180 nm also include several atomic emission lines of nitrogen and oxygen. The UV emissions are due to molecular bands of NO, OH, and N2. The best antimicrobial effect is observed by means of direct plasma treatment. UV and VUV emissions have a lower effect, and there is no difference observed between these two components.

The suitability of a miniaturized non-thermal APPJ operating with Ar at ambient atmosphere for applications related to surface treatment is demonstrated. The VUV emission is measured and the dependence of selected line intensities over the radius of the plasma jet is presented. The Ar discharge is characterized by an intense VUV radiation, attributed to N, H, and O atomic lines along with an Ar2* excimer continuum, which is drastically reduced after adding up to 5% N2 to the Ar working gas. Two absorption dips are found in the VUV spectrum. The surface energy enhancement of substrates at temperatures as low as 35 °C along with chemical reactivity originating from abundant NO and OH free radicals and UV/VUV radiation in the plasma give rise to numerous applications, e.g., in the medical and biological field.

Since several years a number of activities on the field of antimicrobial treatment by using non-thermal plasmas are known. But although there are quite a few plasma based processes commercially available, the complexity of interaction between plasma and micro organisms prevents the breakthrough of this technology up to now. Thus plasma generation and treatment method needs to be adapted for each individual application. The aim of this work is to demonstrate the industrial applicability of plasma technological processes for medical devices. Therefore a non-thermal plasma jet operated in argon at atmospheric pressure and driven by radio frequency (27.12 MHz) is applied to antimicrobial treatment of samples made of heat sensitive materials, such as used in medical devices. Due to its compact design and low power consumption, typical 10 W to 60 W, it is predestined for modularisation. Therefore it can be adapted to nearly any geometry such as given by medical devices to be treated. The plasma is characterised by UV/VIS optical emission spectroscopy. In order to analyse the effect of the plasma on the micro organisms (Bacillus atrophaeus spores and Escherichia coli vegetative bacteria) microbiological tests are performed. First results on lethal effects of the plasma treamtent will be discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The discharge behaviour of a dielectric barrier discharge (DBD) in low-pressure argon gas was investigated by experiments and modelling. The electrical characteristics and light emission dynamics of the discharge were measured and compared with the results of a two-dimensional fluid model. Our investigations showed that the discharge consisted of a single, diffuse discharge per voltage half-cycle. The breakdown phase of the low-pressure DBD (LPDBD) was investigated to be similar to the ignition phase of a low-pressure glow discharge without dielectrics, described by Townsend breakdown theory. The stable discharge phase of the LPDBD also showed a plasma structure with features similar to those of a classical glow discharge. The presence of the dielectric in the discharge gap led to the discharge quenching and thus the decay of the plasma. Additionally, the argon metastable density was monitored by measuring light emission from nitrogen impurities. A metastable density of about 5 ? 1017?m?3 was present during the entire voltage cycle, with only a small (~10%) increase during the discharge. Finally, a reduction of the applied voltage to the minimum required to sustain the discharge led to a further reduction of the role of the dielectric. The discharge was no longer quenched by the dielectrics only but also by a reduction of the applied voltage.

Diffuse dielectric barrier discharges in neon and helium at atmospheric pressure were studied. The discharges were generated between two metal electrodes, both covered by an alumina layer and driven by ac voltage of frequency 10 kHz. The discharge gap was 2.2 mm and 5 mm, respectively. The discharges were investigated by electrical measurements and by temporally and spatially resolved optical emission spectroscopy. The experimental results revealed similar discharge behaviour in both gases being considered. Although the discharges were ignited at slightly different electric field strengths, their evolutions were found to be similar. At maximum discharge current the spatial light intensity distribution was characterized by the formation of a cathode fall. A difference was observed in the magnitudes of the current density only. In addition to the regime with a single discharge pulse per voltage half period T/2, a discharge mode with two and more subsequent current pulses per T/2 (also referred to as the pseudoglow discharge regime in the literature) was obtained due to an increase in the voltage amplitude or an admixture of nitrogen.

The spatially resolved cross-correlation spectroscopy (CCS) was used for systematic investigations of the barrier discharge (BD) in N2/O2 mixtures at atmospheric pressure. The spatio-temporal distributions of the microdischarge (MD) radiation intensities were recorded for the spectral bands of the (0?0) transitions of the 2nd positive (? = 337.1?nm) and 1st negative system of molecular nitrogen (? = 391.4?nm). The velocities of the cathode-directed ionization waves were evaluated from the CCS data. In the middle of the gap, the MD channel diameter was found to be about 0.3?mm and to expand towards both electrodes. On the dielectrics, outward propagating discharges were observed. A computational model of the BD is proposed, to explain the MD formation in short (1?2?mm) air gaps by a Townsend mechanism. The two-dimensional dynamics of the MD development and the channel radiation for the second positive system of nitrogen are simulated. The proposed model explains satisfactorily the experimental results on the velocity of the cathode-directed ionization wave and the MD radiation of the 2nd positive system.

Diffuse barrier discharges (BDs) are characterized by the periodicity of their discharge current and by the uniform coverage of the entire electrode surface by the plasma. Up to now the discharge development, their appearance and dynamics cannot be adequately explained by elementary processes. Different processes are discussed in the literature controversially, in particular the importance of volume and surface processes on the pre-ionization (Penning-ionization, secondary (?-) processes, role of surface charges). Diffuse BDs in nitrogen with small admixtures of oxygen are investigated by plasma diagnostics (current/voltage-oscillography, optical emission spectroscopy) and numerical modelling. Special attention is paid to the transition to the usual filamentary mode, characterized by the presence of micro-discharges and caused by the admixture of oxygen in the range of 0?1200?ppm (parts-per-million). This transition starts at low values of O2 (about 450?ppm) and is introduced by an oscillative multi-peak mode. At higher admixtures (about 1000?ppm) the micro-discharges are generated. According to the results of numerical modelling, secondary electron emission by N2(A?3?u) metastable states plays a major role in discharge maintenance. Due to the much more effective quenching of these states by O2 and NO than by N2 the subsequent delivery of electrons will be decreased when the oxygen amount is increased.

Microdischarges (MDs) of filamentary barrier discharges (BDs) in air and N2/O2 gas mixtures at atmospheric pressure were investigated using the techniques of spatially resolved cross-correlation spectroscopy (CCS) and short exposure time photography (ICCD-camera). The BDs were generated in symmetric discharge cells (configuration of the type 'glass–glass') with two semi-spherical electrodes in order to localize the repetitive MDs at a fixed position. In the case of CCS measurements, the MD development was imaged through spatio-temporal distributions of the radiation intensity of the (0–0) transition of the 2nd positive system of molecular nitrogen (λ = 337 nm). Two-dimensional optical scanning of the MD channel (in the axial and radial directions of the MD) was carried out for a BD operated in a gas mixture consisting of 6 vol% O2 and 94 vol% N2. This gas composition had been found to provide the extremely high stability of the discharge that was necessary for the time-consuming scanning procedure. In the middle of the gap, the MD channel diameter was found to be about 0.3 mm and to expand towards both electrodes. With dielectrics, outward propagating discharges were observed. Short exposure time photos of the MDs taken using an ICCD-camera under the same experimental conditions as for the CCS measurements revealed a branched structure of these discharges on the surfaces, not only on the cathode but on the anode as well. The influence of voltage amplitude on the spatio-temporal distribution of individual MDs of a BD in air was investigated using the CCS-instrument operated in a so-called 'direct start–stop' mode which enabled statistical analysis of the MD sequences within a time range of about 30 µs.

The techniques of spatially resolved cross-correlation spectroscopy (CCS) and current pulse oscillography were used to carry out systematic investigations of the barrier discharge (BD) in the binary gas mixtures N2/O2 at atmospheric pressure. At very low oxygen concentrations (

Barrier discharges (BDs) produce highly non-equilibrium plasmas in a controllable way at atmospheric pressure, and at moderate gas temperature. They provide the effective generation of atoms, radicals and excited species by energetic electrons. In the case of operation in noble gases (or noble gas/halogen gas mixtures), they are sources of an intensive UV and VUV excimer radiation. There are two different modes of BDs. Generally they are operated in the filamentary one. Under special conditions, a diffuse mode can be generated. Their physical properties are discussed, and the main electric parameters, necessary for the controlled BD operation, are listed. Recent results on spatially and temporally resolved spectroscopic investigations by cross-correlation technique are presented. BDs are applied for a long time in the wide field of plasma treatment and layer deposition. An overview on these applications is given. Selected representative examples are outlined in more detail. In particular, the surface treatment by filamentary and diffuse BDs, and the VUV catalyzed deposition of metallic layers are discussed. BDs have a great flexibility with respect to their geometrical shape, working gas mixture and operation parameters. Generally, the scaling-up to large dimensions is of no problem. The possibility to treat or coat surfaces at low gas temperature and pressures close to atmospheric once is an important advantage for their application.

Non-equilibrium plasmas have been intensively studied over the past century in the context of material processing, environmental remediation, ozone generation, excimer lamps and plasma display panels. Research on atmospheric pressure non-equilibrium plasmas intensified over the last two decades leading to a large variety of plasma sources that have been developed for an extended application range including chemical conversion, medicine, chemical analysis and disinfection. The fundamental understanding of these discharges is emerging but there remain a lot of unexplained phenomena in these intrinsically complex plasmas. The properties of nonequilibrium plasmas at atmospheric pressure span over a huge range of electron densities as well as heavy particle and electron temperatures. This paper provides an overview of the key underlying processes that are important for the generation and stabilization of atmospheric pressure non-equilibrium plasmas. The unique physical and chemical properties of theses discharges are also summarized.

The coplanar barrier discharge in synthetic air at 30 kPa pressure was studied by time-correlated single photon counting enhanced optical emission spectroscopy, far-field microscopy enhanced intensified CCD camera and sensitive current measurements. The discharge operated in a regime where two subsequent microdischarges appeared within the same voltage half-period. The electrical analysis of the barrier discharge setup enabled us to quantify charge transfer and the effective electric field development. During the second microdischarge the positive surface streamers follow the interface (triple-line) between the area of deposited charge from the previous one and the area of uncharged dielectric surface. It is shown that additional branching and flashes of surface streamers are responsible for the increased spatial complexity of the deposited surface charges at high overvoltage. A suppressed streamer propagating over the area of deposited surface charge was tracked and the evidence of surface streamer reconnection is presented. A spatiotemporal distribution (resolution of 120 ps and 100 um) of the reduced electric field strength was obtained for both microdischarges from the recorded luminosities of the molecular nitrogen. The reduced electric field of positive streamers in the first microdischarge reached 1200 Td. For the second one, the electric field values for the streamer at the triple-line are slightly lower than that, while for the suppressed streamers are even higher.

The characterization of electrical power distribution in an atmospheric pressure plasma jet operated at six different frequencies is investigated by measurement of input power and voltage-charge plots for the core plasma and the plasma in the effluent. The frequency change is further characterized by measuring the temperature in the effluent at different positions and input power levels. The power input into the core plasma is limited to about 1 W for a wide range of frequencies while the total input power and thus the power input into the effluent increases continuously with frequency.

A streamer-to-spark transition in a self-pulsing transient spark (TS) discharge of positive polarity in air was investigated using cross-correlation spectroscopy. The entire temporal evolution of the TS was recorded for several spectral bands and lines: the second positive system of N2 (337.1 nm), the first negative system of N2+ (391.4 nm), and atomic oxygen (777.1 nm). The results enable the visualization of the different phases of discharge development including the primary streamer, the secondary streamer, and the transition to the spark. The spatio-temporal distribution of the reduced electric field strength during the primary streamer phase of the TS was determined and discussed. The transition from the streamer to the spark proceeds very fast within about 10 ns for the TS with a current pulse repetition rate in the range 8-10 kHz. This is attributed to memory effects, leading to a low net electron attachment rate and faster propagation of the secondary streamer. Gas heating, accumulation of species such as oxygen atoms from the previous TS pulses, as well as generation of charged particles by stepwise ionization seem to play important roles contributing to this fast streamer-to-spark transition.

The micro-discharge properties and evolution in a 2D array of integrated coaxial microhollow dielectric barrier discharges are studied by using highly time-resolved electrical and optical diagnostics. The study is focused on the effect of the gas flow rate and gas residence time on discharge properties. The investigated integrated coaxial microhollow discharge geometry allows operating the discharge at exceptionally small residence times, which can be equal to or even smaller than the discharge period, at reasonable gas flow rates. The gas flow has an impact on gas heating, residual humidity, pre-ionization density and the densities of excited and reactive species produced by previous discharges. A unique voltage–charge plot is obtained with elongated periods without discharge activity. A very significant effect of flow on NO emission is observed that relates to the impact of flow on the NO production in these micro-discharges. Using the emission intensities of molecular bands of the second positive system of nitrogen and the first negative system of the nitrogen ion, effective reduced electric field strengths are obtained with a maximum equal to 870 Td. The reduced electric field decreases with increasing gas flow rate. This behavior is consistent with the reduction of the overall discharge intensity due to a reduced amount of charges present in the discharge gap. Both the flow rate and a reduction in water impurity changing the ion mobility can be responsible for the different effective electric field distributions at the highest and no flow conditions.

This contribution attempts to establish an easy-to-apply non-thermal plasma reactor for efficient toluene removal. Derived from the already established knowledge of the so called Dielectric Barrier Discharge (DBD) Stack Reactor a new model reactor was used in this work. The DBD Stack Reactor is a multi-elements reactor but in this work only one stack element was used to investigate the efficiency and efficacy of toluene removal. In case of reliable results the scalability process for industrial application is already well known. Therefore, laboratory experiments were conducted in dry and wet synthetic air with an admixture of 50 ppm toluene. Along with the toluene removal process the electrical behaviour of the discharge configuration was investigated. It was found that the electrical capacitance of the dielectric barrier changes with variations of the operating voltage. This could be due to the changes in the area of the dielectric barrier which is covered with plasma. Additionally, it was found that the power input into the plasma, at a fixed operating voltage, is proportional to the frequency, which is in agreement with the literature. Regarding the decomposition process, the total removal of toluene was achieved at specific input energy densities of 55 J L-1 under dry conditions and 110 J L-1 under wet conditions. The toluene removal was accompanied by the production of nitric acid (dry conditions) and formic acid (wet conditions). The latter suggested a combination of the plasma reactor with a water scrubber as an approach for total removal of pollutant molecules.

The technique of spatially resolved cross-correlation spectroscopy (CCS) is used to carry out diagnostic measurements of the barrier discharge (BD) in air at atmospheric pressure. Quantitative estimates for electric field strength E(x,t) and for relative electron density ne(x,t)/nemax are derived from the experimentally determined spatio-temporal distributions of the luminosity for the spectral bands of the 0-0 transitions of the second positive system of N2 (λ = 337.1 nm) and the first negative system of N2+ (λ = 391.5 nm). These results are used to test the validity of some physical models of electrical breakdown in a BD. The influence of the spatio-temporal structure of the discharge on the chemical kinetics of ozone synthesis is studied by means of a semi-empirical method based on the results of spatially resolved CCS measurements.

This review summarizes the state of the art of plasma diagnostics on atmospheric pressure plasmas formed at characteristic length scales of approximately 1 mm or smaller and identifies challenges and prospects. Both plasmas generated in confined geometries, so-called microplasmas, as well as discharge filaments occurring in commonly filamentary plasmas, e.g. microdischarges in dielectric barrier discharges are covered. In spite of the differences between microplasmas which often obtain a quasi steady-state and single microdischarges or filaments which are self-limited in space and time and thus intrinsically transient, both face very similar diagnostic challenges of which two are immediately apparent: the high collisionality which requires adaptations of standard plasmas diagnostics often developed for low-pressure plasmas, and the requirements on high spatial resolution due to the strong gradients in plasma properties. The complexity of the plasma generation and the physical and chemical properties of the above-mentioned plasmas requires the knowledge of an extensive series of different parameters to obtain a full characterization. As the results of the diagnostics are not always unambiguous and require a detailed understanding of plasma physics and chemistry, a summary of the main properties and pecularities of high-pressure plasmas is included in this review.

The inactivation of bacteria suspended in liquids by an atmospheric pressure plasma is a complicated and yet not well understood process, due to several constituents of the "plasma cocktail" in the plasma/gas phase which can contribute to bacteria inactivation and the transport and chemistry processes of the created species in the liquid phase. To investigate the main players in the bacteria inactivation processes we use a RF atmospheric pressure plasma jet which is used for remote bacteria treatment. The plasma jet is constructed to allow accurate power measurements. Mass spectrometry, optical emission spectroscopy as well as electrical diagnostics have been used to investigate the amount of charged and reactive species and UV-emission reaching the water surface. We show that with the chosen treatment conditions, reactive species (ROS and RNS) concentrations and probably (V)UV emission are high enough to induce chemistry in the liquid phase leading to bacteria inactivation, while the electric field and charged particles are too low to induce observed effects. To further determine the role of the reactive species interaction within the liquid, nitrite, nitrate and hydrogen peroxide concentrations have been obtained by ion chromatography and colorimetric methods. Combined with measured and estimated values of the reactive species in the gas phase we use a 0D-solution kinetics model to calculate other species expected in the liquid phase and important for bacteria inactivation, which have not been measured. We show that the obtained concentrations of HNO2, ONOO and H2O2 are in the same range as reported values in literature of the minimum inhibitory and bactericidal concentrations.

Summary form only given. The application of atmospheric pressure discharges in new fields like environmental protection, surface treatment or life-sciences requires a profound knowledge on the plasma parameters and properties. This includes (1) the characterization of the breakdown processes triggering plasma chemistry, (2) the proper determination of the electrical parameters and (3) the description of the dominant chemical pathways. The contribution aims to present new approaches regarding these three topics for pulsed driven Dielectric Barrier Discharges in particular. It will be shown by fast electrical, optical and spectroscopic methods that the ignition, breakdown statistics and spatio-temporally resolved development of pulsed DBD microdischarges is controlled by the properties of the power supply (duty cycle, frequency, amplitude varied) as well as the composition of the gas1. In particular the starting point of the microdischarge ignition can be changed which is a new effect in DBDs caused by electric field rearrangement in the gap due to positive ion development. Surface processes at the dielectric barriers influencing this behavior will be discussed, too. The determination of electrical parameters such as discharge current, gas gap voltage, instantaneous power and energy as well as the charge transferred through the gas gap based on a simple equivalent circuit will be presented. The proposed approach accurately accounts the displacement current and key capacitance values, which inexactly determination are a source of experimental errors in particular in case of pulsed driven DBDs. The presented approach is consistent with sinusoidal-voltage driven or miniature pulsed driven DBDs. We believe that these new insights on electrical characterization are an important input for those who are working with DBDs, since the electrical parameters are mandatory information. The characterization of the dominant chemical pathways of advanced plasma processes is usually focused on the volume processes only. This contribution will discuss several examples which shall emphasize, that secondary effects must be considered, too. These shall cover the topics of adsorption-enhanced VOC conversion by DBD plasma treatment, NOx conversion and indirect plasma treatment of liquids for antimicrobial and chemical decontamination.

The application of atmospheric pressure discharges in new fields like environmental protection, surface treatment or life-sciences requires a profound knowledge on the plasma parameters and properties. This includes the characterization of the breakdown processes triggering plasma chemistry, the proper determination of the electrical parameters and the description of the dominant chemical pathways. This contribution aims to present new approaches regarding these three topics for pulsed driven Dielectric Barrier Discharges (DBDs) in particular. Fast electrical, optical and spectroscopic methods enable the study of ignition, breakdown statistics and spatio-temporally resolved development of pulsed DBD microdischarges. The determination of electrical parameters such as discharge current, gas gap voltage, instantaneous power and energy as well as the charge transferred through the gas gap is based on a simple equivalent circuit which is consistent with sinusoidal-voltage driven or miniature pulsed driven DBDs. The characterization of the dominant chemical pathways of advanced plasma processes discusses also several examples including secondary effects, such as adsorption-enhanced VOC conversion by DBD plasma treatment.

A time modulated radio frequency (RF) plasma jet operated with an Ar mixture is investigated by measuring the electron density and electron temperature using Thomson scattering. The measurements have been performed spatially resolved for two different electrode configurations and as a function of the plasma dissipated power and air concentration admixed to the Ar. Time resolved measurements of electron densities and temperatures during the RF cycle and after plasma power switch-off are presented. Furthermore, the influence of the plasma on the air entrainment into the effluent is studied using Raman scattering. (C) 2013 AIP Publishing LLC.

It is demonstrated that a four-wave mixing technique based on coherent anti-Stokes Raman spectroscopy (CARS) can determine the electric field strength of a pulsed-driven filamentary dielectric barrier discharge (DBD) of 1 mm gap, using hydrogen as a tracer medium in nitrogen at atmospheric pressure. The measurements are presented for a hydrogen admixture of 10%, but even 5% H2 admixture delivers sufficient infrared signals. The lasers do not affect the discharge by photoionization or by other radiation-induced processes. The absolute values of the electric field strength can be determined by the calibration of the CARS setup with high voltage amplitudes below the ignition threshold of the arrangement. This procedure also enables the determination of the applied breakdown voltage. The alteration of the electric field is observed during the internal polarity reversal and the breakdown process. One advantage of the CARS technique over emission-based methods is that it can be used independently of emission, e.g. in the pre-phase and in between two consecutive discharges, where no emission occurs at all.

To face the worldwide problem of anthropogenic carbon dioxide (CO 2 ) emission new techniques have to be developed. One approach for carbon capture utilization (CCU) is the conversion of CO 2 to more valuable chemicals, e.g., carbon monoxide (CO) by means of non-thermal plasma generated at ambient conditions and supplied by excess energy from renewable sources. This paper reports about the effect of the admixture of inert gases, namely nitrogen or argon to CO 2 in a coplanar dielectric barrier discharge (DBD). Systematic experiments were conducted to investigate the effects of applied voltage, frequency, flowrate and CO 2 concentration in the influent. The composition of products, energy efficiency and yield were determined. Within the investigated parameter ranges, the maximum conversion of CO 2 to CO efficiency of 1% was achieved when the specific input energy was 190 J L -1 , whereas the maximum CO yield of 0.7% was achieved when the specific input energy was 210 J L -1 . In conclusion, the energy efficiency can be significantly increased by operating the plasma in a diluted CO 2 gas.

Using theoretical and experimental methods, the electric field and the electron multiplication in direct vicinity of a sharp cathode is analysed. The development of the electric field in the pre-breakdown phase of the atmospheric pressure air negative DC corona discharge in the Trichel pulse regime is determined. During the following ultra-fast electrical breakdown, the emission of selected spectral bands of the nitrogen molecule is recorded with high spatiotemporal resolution using the time-correlated single photon counting method. The emission of a Townsend discharge is used to calibrate the setup for the quantitative determination of electric field. Therefore, the Trichel pulse corona and Townsend discharge cell are arranged in the same single-table setup. This direct calibration procedure is described step-by-step including the discussion of known limitations. Finally, the electric field development of the positive streamer passing the 160 microns distance in less than two nanoseconds is determined. Due to the high spatiotemporal gradients of the electric field strength within the streamer breakdown, the local field approximation of the electron component is analysed by investigating numerically the temporal and spatial electron relaxation by means of the solution of the electron Boltzmann equation and Monte Carlo simulation. Results of these computations are given for several reduced electric field values and prove that the electrons are in a hydrodynamic equilibrium state for experimentally given space and time scales for reduced elds above 100 Td.

A time-correlated single-photon counting technique was used to verify the formation of a cathode-directed streamer inside the narrow cathode region following the interpulse phase of regular negative corona Trichel pulses in ambient air. A purely experimental approach was used to determine the spatiotemporal development of the electric field during the Trichel pulse rise with an extremely high resolution of 10 μm and tens of picoseconds. The results confirm the positive-streamer mechanism for Trichel pulse formation and provide supportive evidence for the hypothesis that the formation of a primary cathode-directed streamer occurs always in any streamer-initiated breakdown and prebreakdown phenomena associated with cathode spot formation.

Summary form only given. The treatment of liquid with a surface dielectric barrier discharge (DBD) under atmospheric pressure in air results in pH decrease and generation of nitrate (NO 3 −), nitrite (NO 2 −) and hydrogen peroxide (H 2 O 2 ) in water. Even, after plasma treatment antimicrobial effects on suspended microorganisms were investigated [1] [2].

Summary form only given. There is an increasing interest in atmospheric pressure discharges for technological applications. Due to their low gas temperature, high electron energy and the presence of active species these discharges have a high potential for plasma chemistry e.g. for ozone production as well as gas and water purification1. Besides corona discharges and micro hollow cathode discharges, dielectric barrier discharges are often used in this field of application. Here, sinusoidal driven ones are basically used in practice. In last years however, there are applications where pulsed driven discharges show a better efficiency in plasma-chemical application (e.g. ozone generation2) than sinusoidal driven ones. This finding forces systematic studies in this matter.

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.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.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.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.

Plasma-induced inactivation of bacteria in aqueous liquids is supported by acidic pH and accompanied by generation of low-molecular chemical species which are detected as nitrate, nitrite and hydrogen peroxide. To get more insight into mechanisms of change of liquid composition by plasma treatment as well as transmission of bactericidal plasma effects into aqueous liquids, bactericidal effects under different plasma-treatment conditions and liquid analytics are combined with theoretical considerations to focus possible reaction channels of plasma-water interactions.

Nowadays non-thermal plasma technologies are state of the art for the generation of ozone as an important oxidant for water cleaning or bleaching, the incineration of waste gases or for the removal of dust from flue gases in electrostatic precipitators. Furthermore their possibilities of gas depollution are well known. Plasmas contain reactive species, in particular ions, radicals or other oxidizing compounds, which can decompose pollutant molecules, organic particulate matter or soot. Electron beam flue gas treatment is another plasma-based technology which has been successfully demonstrated on industrial scale coal fired power plants. This chapter aims a comprehensive description of plasma-based air remediation technologies. The possibilities of exhaust air pollution control by means of non-thermal plasmas generated by gas discharges and electron beams will be summarized. Therefore plasma as the 4th state of matter, its role in technology and the principle of plasma-based depollution of gases the will be described. After an overview on plasma-based depollution technologies the main important techniques, namely electron beam flue gas treatment, gas discharge generated plasmas including plasma-enhanced catalysis and injection methods will be described in separate sections. In these sections selected examples of commercially available or nearly commercialised processes for flue gas treatment or the removal of volatile organic compounds and deodorization will be described, too. Current trends and concepts will be discussed.

The investigation of striated microdischarges in barrier discharges in argon at atmospheric pressure is reported. Microdischarges were investigated by means of electrical measurements correlated with intensified CCD camera imaging. The scaling law theory known from low-pressure glow discharge diagnostics was applied in order to describe and explain this phenomenon. The investigated microdischarge is characterized as a transient atmospheric-pressure glow discharge with a stratified column. It can be described by similarity parameters $i/r\ensuremath{\approx}0.13$ A/cm, $pr\ensuremath{\approx}5$ Torr cm, and $3l\ensuremath{\lambda}/rl5$ with the current $i$, pressure $p$, interval of subsequent striations $\ensuremath{\lambda}$, and radius of the plasma channel $r$. An attempt to describe the mechanism of creation of a striated structure is given, based on an established model of the spatial electron relaxation.

DBD plasma treatment of non-buffered water based liquids under atmospheric conditions resulted in microorganism inactivation accompanied by acidification as well as generation of nitrite, nitrate, and hydrogen peroxide1. In an additional study, microorganisms were incubated with sodium chloride solution immediately as well as 30 min after DBD plasma treatment of the liquid. An effective inactivation was found under these conditions, too. These results led to the conclusion that microorganism inactivation was caused mainly by stable reactive species generated in the liquid as a result of plasma treatment. More detailed investigations using variable liquid volumes and surfaces demonstrated that acidification as well as generation of nitrite, nitrate, and hydrogen peroxide proceeds at the gas-liquid interface. A subsequent distribution in the bulk liquid seems to be caused both by diffusion and convection processes. However, addition of nitrite, nitrate, hydrogen peroxide or acid alone or as mixtures to microorganism suspensions did not cause any biological effects. Using additional results of liquid treatment by atmospheric pressure plasma in an argon enriched atmosphere instead of air, possible mechanisms as well as stable reactive species being responsible for biological effects like microorganism inactivation are discussed.

Inadequately performed hand hygiene and non-disinfected surfaces are two reasons why the keys and mouse-buttons of laptops could be sources of microbial contamination resulting consequently in indirect transmission of potential pathogens and nosocomial infections. Until now the question has not been addressed whether the ventilation-blowers in laptops are actually responsible for the spreading of nosocomial pathogens. Therefore, an investigational experimental model was developed which was capable of differentiating between the microorganisms originating from the external surfaces of the laptop, and from those being blown out via the ventilation-blower duct. Culture samples were taken at the site of the external exhaust vent and temperature controls were collected through the use of a thermo-camera at the site of the blower exhaust vent as well as from surfaces which were directly exposed to the cooling ventilation air projected by the laptop. Control of 20 laptops yielded no evidence of microbial emission originating from the internal compartment following switching-on of the ventilation blower. Cultures obtained at the site of the blower exhaust vent also showed no evidence of nosocomial potential. High internal temperatures on the inner surfaces of the laptops (up to 73°C) as well as those documented at the site of the blower exhaust vent (up to 56°C) might be responsible for these findings., GMS Krankenhaushygiene Interdisziplinär; 5(2):Doc07; ISSN 1863-5245

The technological potential of non-thermal plasmas for the antimicrobial treatment of heat sensitive materials is well known and has been documented in a great number of research activities, but the realisation of industrial plasma-based decontamination processes remains a great challenge. One of the reasons for this situation is the fact that an antimicrobial treatment process needs to consider all properties of the product to be treated as well as the requirements of the complete procedure, e.g. a reprocessing of a medical instrument. The aim of the BMBF-funded network project PLASMOSE is to demonstrate the applicability of plasma-based processes for the antimicrobial treatment on selected, heat sensitive products. Modular and selective plasma sources, driven at atmospheric pressure are used. This basic approach shall combine the technological advantages of atmospheric pressure plasmas (avoidance of vacuum devices and batch processing) with the flexibility and handling properties of modular devices. Two different objectives were selected: the outer surface treatment of medical products and the treatment of hollow packaging for pharmaceutical products. The outer surface treatment of medical products, in particular catheters for intracardial electrophysiological studies, is investigated by means of RF-driven plasma jets in argon. Due to its compact design they are predestined for modularisation and can be adapted to nearly any complex 3-dimensional structure as given by the medical products. The realisation of an antimicrobial treatment process of hollow packaging for pharmaceutical products has quite different demands. Such a process is needed to be implemented in in-line filling procedures and to work without additional process gases. The idea is to use an atmospheric air, microwave-driven self propagating discharge. The plasma process is optimized for the decontamination of 200 ml bottles by field simulation studies combined with optical emissions spectroscopy and micro-biological tests. Das technologische Potential von nicht-thermischen Plasmen zur antimikrobiellen Behandlung von thermolabilen Materialien wurde in einer großen Zahl von Forschungsarbeiten dokumentiert, die Realisierung in einem industriellen plasmabasierten Dekontaminationprozess bleibt aber eine große Herausforderung. Einer der Gründe für diese Situation ist die Tatsache, dass ein antimikrobieller Prozess sowohl alle Anforderungen des Produkts als auch die des gesamten Aufbereitungsprozesses, z.B. eines medizinischen Instruments, berücksichtigen muss. Ziel des durch das BMBF geförderten Verbundprojekts PLASMOSE (Plas magestützte Oberflächenmodifizierung mittels mo dularer se lektiver Plasmaquelle ) ist der Nachweis der Anwendbarkeit eines plasmabasierten Prozesses zur antimikrobiellen Behandlung von thermolabilen Produkten. Dazu werden modulare selektive Plasmaquellen bei Atmosphärendruck eingesetzt. Der Ansatz beruht auf der Kombination der technischen Vorteile eines Atmosphärendruckplasmas mit den Vorteilen bzgl. der Flexibilität und der Handhabungseigenschaften von modularen Vorrichtungen. Zwei unterschiedliche Aufgaben wurden als Zielstellung ausgewählt: die Außenbehandlung von Medizinprodukten und die Innenbehandlung von Hohlkörpern als Primärverpackung für pharmazeutische Produkte. Die Behandlung der äußeren Oberflächen von Medizinprodukten, in diesem Fall Kathetern für intrakardiale elektrophysiologische Untersuchungen, wurde mittels eines RF angeregten Plasmajets in Argon durchgeführt. Aufgrund seiner kompakten Ausführung ist er prädestiniert für eine Modularisierung und kann dadurch nahezu an jede dreidimensionale Struktur angepasst werden. Die Realisierung der antimikrobiellen Behandlung der als Primärverpackung dienenden Hohlkörper hat deutlich andere Prozessanforderungen. Dieser Prozess muss in einer mit hohen Taktraten arbeitenden Abfüllmaschine integrierbar sein und darf aus Kostengründen keine teuren Arbeitsgase benötigen. Daher wurde zur Realisierung eine mikrowellenangeregte Laufentladung eingesetzt, die in Umgebungsluft arbeitet. Der Prozess wurde für die Behandlung von 200 ml PET Flaschen optimiert. Hierzu wurden sowohl Simulationen des elektrischen Feldes als auch optische Emissionsspektroskopie durchgeführt. Begleitet wurden diese Untersuchungen durch mikrobiologische Tests zur Bestimmung der Abtötungskinetik.