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A semi-analytical model is presented for the determination of the electric field in reactors used for cold atmospheric pressure plasma (CAPP) jet production, based on the concept of dielectric barrier discharge (DBD). These systems are associated with various applications in contemporary engineering, ranging from material processing to biomedicine, and at the same time they provide many challenges for fundamental research. Here, we consider a simplified system configuration of a single driven electrode, surrounding a thin dielectric tube, which does not contribute to the electric field, since the potential variation is immediate due to its negligible size. By employing the cylindrical coordinate system that perfectly fits the present plasma jet reactor, we separate the area of electric activity into three distinct domains according to the imposed external conditions, while our analysis is restricted to the electrostatic limit of Maxwell’s equations. To this end, cylindrical harmonic field expansions are used for the potential, which produce the corresponding electric fields in each subdomain. Due to the imposed mixed-type boundary value problem, additional linear terms are incorporated, leading to three possible analytical solutions of the physical problem under consideration. The efficiency of the method is demonstrated by comparing the final formulae with a numerical solution, followed by the relevant discussion.

The impact of titanium dioxide (TiO2) on the physical properties of poly(lactic acid) (PLA) is explored, along with the combined effect of Atomic Layer Deposition of zinc oxide (ZnO) on the nanocomposite films' surface. PLA/TiO2 bionanocomposites are prepared via melt‐extrusion and characterized in terms of their morphological, thermal, and mechanical properties. Homogeneous dispersion of the filler offers enhanced mechanical performance for samples up to 5 wt% in TiO2 content. Thermal stability of PLA is also slightly improved upon increasing TiO2 content. This work also demonstrates that surface modification of PLA/TiO2 films employing Atomic Layer Deposition of zinc oxide enhances hydrophobicity, while antimicrobial activity, although mild, appears enhanced for coated samples. Water vapor permeability is retained in both coated and uncoated nanocomposites. Surface characterization of the studied specimens, by x‐ray photoelectron spectroscopy and scanning electron microscopy, reveals subsurface diffusion and reaction of the depositing compounds within PLA, leading to a different surface chemistry involving Zn(OH)2. This study gives valuable insights on the parameters affecting the atomic layer deposition of inorganic coatings on a polymeric substrate in the presence of nanoinclusions and, therefore, on the physical properties of the coated films, providing the pathway for their exploitation in food packaging applications. [ABSTRACT FROM AUTHOR]

This work is devoted to unbuffered and buffered water treatment by means of atmospheric pressure cold plasma of electrical discharges. The interest in the activation of these two liquids by plasma-induced, gaseous-phase chemistry ranges over a wide area of potential applications and interdisciplinary scientific fields. These include biology, medicine, sanitation, environmental restoration, agriculture, etc. Atmospheric pressure cold plasma is here produced in the form of a plasma jet and set into physical contact with the liquid specimens. The operational window of the treatment, in terms of plasma reactivity, is determined by means of UV-NIR optical emission spectroscopy, and the treated liquids are probed in a variety of respects. Evaporation rate, temperature, acidity and basicity, resistivity, and oxidation-reduction potential are measured as a function of the treatment time, either in-situ or ex-situ. The formation of principal reactive oxygen species, i.e., •OH, H2O2 and O 2 • − , with a plasma jet mean power lower than 400 mW, is eventually demonstrated and their concentration is measured with original methods borrowed from the biology field. The experimental results are linked to reports published over the last ten years, which are compiled in a brief but meaningful review. [ABSTRACT FROM AUTHOR]

This report gives prominence to the importance of the traditional Cockcroft–Walton voltage multiplier to the design of pulsed power supplies for dielectric barrier discharge (DBD) applications. Following an inventive concept, a simple Cockcroft–Walton generator is combined with a MOSFET-based switch (in either “push” or “pull” mode). Thus, the to-be-chopped stabilized dc high voltage is produced by a compact, transformer-less, modular unit, having high flexibility in terms of engineering. This approach leads to well-defined, square, high-voltage pulses of variable amplitude, frequency, and duty cycle. Design, implementation, and proof test of such a prototype are here demonstrated. The prototype yields square pulses as high as 10 kV (plateau value), as narrow as 350 ns (variable pulsewidth up to millisecond, depending on the frequency), rising or falling time close to 20 ns, pulse repetition rates up to 4 kHz, and output mean power up to 150 W. The functionality of the system is demonstrated by driving coaxial, ambient air DBDs of variable lengths, while principal electrical and optical parameters are recorded. Peak power values higher than 70 kW are measured on the DBD side, while the voltage multiplier power efficiency factor remains close to 95%. [ABSTRACT FROM AUTHOR]

The role of the plasma electrode (PE) bias in the extraction process in a large-volume hybrid multicusp negative-ion source, which is driven by 2.45-GHz microwaves, is studied. Spatially resolved negative-ion and electron density measurements close to the extractor aperture were performed under various pressures (1-4 mtorr) by means of the electrostatic probe and photodetachment technique. As the low positive voltage applied to the PE is slightly increased (from 4 to 7 V), the electron temperature passes through a minimum (0.2-0.6 eV), while simultaneously, both the negative-ion density and the [H.sup.-] extracted current reach a maximum (~1-2 x [10.sup.9] [cm.sup.-3] and ~0.5 mA/c[m.sup.2], respectively). Optimum pressure values for the extracted negative-ion current and the negative-ion density are found between ~1.5 and 3 mtorr. It is deduced that the negative-ion density measured in the center of the source cannot be directly correlated with the ion extracted current. The electron density and the associated extracted electron current linearly decrease as a function of the PE bias. The physical mechanisms explaining the experimental results are discussed. Index Terms--Electrostatic probe, hydrogen, microwaves, negative ions, photodetachment, plasma electrode (PE) bias.

In the present work, a single dielectric barrier discharge (SDBD)-based actuator is developed and experimentally tested by means of various diagnostic techniques. Flexible dielectric barriers and conductive paint electrodes are used, making the design concept applicable to surfaces of different aerodynamic profiles. A technical drawing of the actuator is given in detail. The plasma is sustained by audio frequency sinusoidal high voltage, while it is probed electrically and optically. The consumed electric power is measured, and the optical emission spectrum is recorded in the ultraviolet–near infrared (UV–NIR) range. High-resolution spectroscopy provides molecular rotational distributions, which are treated appropriately to evaluate the gas temperature. The plasma-induced flow field is spatiotemporally surveyed with pitot-like tube and schlieren imaging. Briefly, the actuator consumes a mean power less than 10 W and shows a fair stability over one day, the average temperature of the gas above its surface is close to 400 K, and the fluid speed rises to 4.5 m s−1. A long, thin layer (less than 1.5 mm) of laminar flow is unveiled on the actuator surface. This thin layer is interfaced with an outspread turbulent flow field, which occupies a centimeter-scale area. Molecular nitrogen-positive ions appear to be part of the charged heavy species in the generated filamentary discharge, which can transfer energy and momentum to the surrounding air molecules. [ABSTRACT FROM AUTHOR]

Biosolids contain high amounts of human pathogenic bacteria that are excreted in feces and urine. The enteric pathogenic bacteria Salmonella sp., Escherichia coli (enteropathogenic and enterotoxigenic variants), coliforms, Clostridium sp., Campylobacter sp., Listeria sp., and Yersinia sp., might be present in biosolids. A large proportion of these bacteria are both human pathogenic and zoonotic, which means that they can cause infections in both humans and animals. In addition, these organisms have a strong ability to persistently adapt to changes in the surrounding environment. According to the 86/278 EC Directive on the protection of the environment and of the soil when sewage sludge is used in agriculture, the minimum requirement for alternative treatments to produce sanitized sludge is defined as containing <500 colony forming units E. coli/g (cfu/g) and 0 Salmonella sp. in 50 g wet weight. This study reviews the current technologies employed for the reuse of treated biosolids in agriculture and unveils an emerging process that could lead to pathogenic microorganism reduction. The process refers to atmospheric pressure air cold plasma of electrical discharges and appears to be an effective treatment with the potential to destroy pathogenic cells of disease-causing and antibiotic-resistant bacteria, such as E. coli, coliforms, and Salmonella sp. of different serotypes. [ABSTRACT FROM AUTHOR]

This paper is devoted to the design, implementation, and test of a low cost, modular, and reliable pulsed high-voltage (HV) converter (dc chopper). The distinct characteristics of the present prototype refer to: adjustable voltage amplitude up to 7 kV, amplitude drop less than 4‰ for $2 \times 10$ A output peak current at 5 kHz, adjustable pulse frequency up to 5 kHz, adjustable duty cycle between 1% and 10%, rising/falling time around 100 ns, and jitter about 10 ns. In principle, 1-kV modules based on a fast MOSFET each are combined in series to form a completely modular push–pull switch configuration. Contrary to sophisticated optical fiber-based insulation techniques, the driving low-voltage stage of the power supply is magnetically coupled to the HV stage. The low-voltage stage defines and schedules the HV pulses by means of a microcontroller. The 7 kV is equally distributed along MOSFETs due to balancing networks of passive components. Zener diodes in parallel with MOSFETs provide sufficient protection against overvoltages. The power supply has been successfully tested on dielectric-barrier discharge-based plasmas which have nowadays continuous technological interest. [ABSTRACT FROM AUTHOR]

Laser-induced fluorescence diagnostic technique is applied here to probe xenon neutrals and single-charged ions in an ambipolar plasma source. A single tunable diode laser is employed for pumping both following transitions: $6s{~}^{\mathrm {2}} {[{1/2}]}_{\mathrm {1}}^{\mathrm {0}}$ – $6p{~}^{2} {[{3/2}]}_{\mathrm {1}}^{\mathrm {0}}$ (centered at 834.68 nm; air) and $5d{\mathrm {[{4}]}}_{\mathrm {7/2}}$ – $6p{\mathrm {[{3}]}}_{\mathrm {5/2}}$ (centered at 834.72 nm; air), for Xe I and Xe II detection, respectively. The corresponding decay states are $6s{\mathrm {[{3/2}]}}_{\mathrm {1}}^{\mathrm {0}}$ and $6s{\mathrm {[{2}]}}_{\mathrm {3/2}}$ leading to fluorescence signal at 473.415 and 541.915 nm, respectively. A detailed description of the experimental setup along with time-averaged fluorescence signals are presented, demonstrating the possible application of the above adjacent pumping wavelengths in xenon ambipolar plasmas for probing both ions and neutrals under various operating conditions. A comprehensible discussion to what extent the registered laser-induced fluorescence signals mirror velocity distribution functions is realized, following hyperfine splitting and isotopic shift analysis. [ABSTRACT FROM AUTHOR]

Benchmarking and validation are prerequisites for using simulation codes as predictive tools. In this work, we have developed a Global Model for Negative Hydrogen Ion Source (GMNHIS) and performed benchmarking of the GMNHIS against another independently developed code, Global Enhanced Vibrational Kinetic Model (GEVKM). This is the first study to present a quite comprehensive benchmarking test of this kind for models of negative hydrogen ion sources (NHIS), and excellent agreements have been achieved for collisional energy loss per electron-ion pair created, electron number density, electron temperature, densities of H 3 + and H 2 + ions, and densities of H(n = 1–3) atoms. Very small discrepancies in number densities of H − ions and H + ions, as well as the vibrational distribution function of hydrogen molecules, can be attributed to the differences in the chemical reactions datasets. The GEVKM includes additional chemical reactions that are more important at high pressures. In addition, we validated the GMNHIS against experimental data obtained in an electron cyclotron resonance discharge used for H − production. The model qualitatively (and even quantitatively for certain conditions) reproduces the experimental H − number density. The H − number density as a function of pressure first increases at pressures below 1.6 Pa and then saturates for higher pressures. This dependence was analyzed by evaluating contributions from different reaction pathways to the creation and loss of the H − ions. The developed codes can be used for predicting the H − production, improving the performance of NHIS, and ultimately optimizing the parameters of negative ion beams for fusion reactors. [ABSTRACT FROM AUTHOR]

The role of lamellarity and composition of liposomal membranes in the degree of their disruption by plasma bullets is investigated. Multilamellar and unilamellar vesicle liposomes consisted of phosphatidylcholine, different amounts of cholesterol, and encapsulating calcein as a reporter molecule, are prepared. Plasma-induced release of calcein from liposomes is used for evaluating the degree of plasma influence on the lipid bilayers. Presence of cholesterol in liposomal membranes below 50 mol%, results in increased disruption by the plasma, while liposomes with 50 mol% cholesterol are resistant. Addition of negative charged lipid in the liposomes (which results in vesicles with negative zeta-potential) makes them more labile to the plasma and induces post-treatment effects. Finally, it is clearly demonstrated that unilamellar liposomes are readily disordered by the plasma, as compared to multilamellar ones. [ABSTRACT FROM AUTHOR]

In this paper, a dielectric-barrier discharge (DBD) of Ar:\N2 mixtures at atmospheric pressure is studied in relation to plasma jet production. The discharge takes place in a capillary dielectric tube, and it is sustained by positive high-voltage pulses. It is herein claimed that, apart from the traditional DBD (which is developed perpendicularly to the gas flow and can produce afterglows), plasma jet propagates simultaneously parallel to the gas flow due to ionization waves guided by the dielectric tube. A quite simple electrical model is applied to simulate the proposed DBD and plasma jet coexistence. The concept of capacitive behavior of both barrier discharge and jet is taken into account. This model in combination with UV–visible optical emission spectroscopy and conventional photography supports the aforementioned statements. The dependence of the jet domination against the afterglow on the gas mixture is demonstrated, and the \N2 additive at 2.5 \%–3\% in Ar is found to be the most efficient for jet production. The model runs with the measured interelectrode voltage as input and yields the circuit total current as output. Matching between the measured current and the model output is attempted by adjusting two free parameters. This tuning of the free parameters provides reliable values for the electrical components of the model. Thus, a simple mean for realistic representation of both DBD and jet is achieved. This tool could be applied to the design of plasma jet reactors. [ABSTRACT FROM PUBLISHER]

The role of the plasma electrode (PE) bias in the extraction process in a large-volume hybrid multicusp negative- ion source, which is driven by 2.45-GHz microwaves, is studied. Spatially resolved negative-ion and electron density measurements close to the extractor aperture were performed under various pressures (1-4 mtorr) by means of the electrostatic probe and photodetachment technique. As the low positive voltage applied to the PE is slightly increased (from 4 to 7 V), the electron temperature passes through a minimum (0.2-0.6 eV), while simultaneously, both the negative-ion density and the H- extracted current reach a maximum (~1-2 × 109 cm-3 and ~0.5 mA/cm2, respectively). Optimum pressure values for the extracted negative-ion current and the negative-ion density are found between ~1.5 and 3 mtorr. It is deduced that the negative-ion density measured in the center of the source cannot be directly correlated with the ion extracted current. The electron density and the associated extracted electron current linearly decrease as a function of the PE bias. The physical mechanisms explaining the experimental results are discussed. [ABSTRACT FROM AUTHOR]

Hereby, five dipolar electron cyclotron resonance elementary sources are assembled to form a 2D network for H− negative ion production. The resultant magnetic field of the network is considered by means of numerical and experimental data, and an artistic photo of the produced plasma is presented. Laser photodetachment measurements in these plasmas confirm the applicability of such networks to this specific purpose. [ABSTRACT FROM PUBLISHER]

This paper is devoted to the study of gas flow fields related to helium atmospheric pressure guided streamer (plasma bullet) propagation in the air. For very weak up to moderate helium flows, the modification induced to the gas flow field by the plasma ignition is demonstrated; it is shown that the turbulent flow region is expanded and two conditions must be fulfilled regarding the working gas profile in the air for streamer propagation, i.e., laminar flow and high concentration in this laminar flow region. [ABSTRACT FROM PUBLISHER]

Herein, a plasma microjet of argon–nitrogen mixtures is produced at atmospheric pressure. The device operation is based on a dielectric-barrier discharge generated by high-voltage positive pulses. We show the possibility to direct the excited species of the jet into flexible silicone tubes and to drastically modify the reactivity at the tube's downstream end by varying the gas composition of the jet. The induced modifications are illustrated by aesthetically pleasing images which unveil the existence of an optimum proportion of nitrogen to argon in order to achieve increased reactivity. [ABSTRACT FROM AUTHOR]

The outlet of a plasma microjet system operating with noble gases at atmospheric pressure is connected to dielectric guides, and the transfer of excited species to long downstream regions is demonstrated by means of photography. Both straight and curved particle propagation paths are achieved and illustrated by imaginative images. The latter justify the potential use of this atmospheric-pressure plasma device to biomedical applications. [ABSTRACT FROM AUTHOR]

Anodic dc arc discharge in water is herein used as an efficient medium for production of nanomaterials with high technological interest. The plasma created mainly consists of ionized and excited species of dissociated water and evaporated element of the anode electrode. Depending on the anode material, diverse and compelling crystalline nanostructures are formed, probably initiated by the supersaturation processes taking place in the plasma phase. This physical effect is visualized by the images presented in this paper. [ABSTRACT FROM AUTHOR]

Argon plasma jet is generated at atmospheric pressure under monopolar pulsed conditions. Images demonstrating luminous activity due to excited gaseous species are presented in combination with voltage-current waveforms in nanosecond scale. The jet is physically altered (length, diameter, and luminosity) as a function of two electrical parameters, i.e., the amplitude and frequency of the high voltage applied. Temperature measurements indicate the potential use of this system to diverse surface treatments, laying from biomedical applications at room temperature to inert material modification where thermal effect is a prerequisite. [ABSTRACT FROM AUTHOR]

Point-to-plane dc glow discharge has been proposed as an efficient medium for polymer treatment in terms of surface chemistry. However, this discharge is greatly modified when polymer samples are introduced. The study of the differences between the pristine discharge and that with polymer is essential for chemical process optimization. Herein, macroscopic observations by means of photography provide insight to the physical aspects of these differences. [ABSTRACT FROM AUTHOR]

Front Cover: Atmospheric‐pressure plasmas or more precisely Atmospheric‐Pressure Guided Streamers (APGSs) of electrical discharges are chemically active media of low temperature. This reactive environment is a promising tool for biomedical applications, and we recently proposed liposomes (LIPs) as a simple in vitro model to study interactions between cells and APGSs; herein we evaluate the effect of APGSs on LIPs with various composition, size and number of bilayers. Further details can be found in the article by Panagiotis Svarnas, Sophia G. Antimisiaris et. al. on page 655. [ABSTRACT FROM AUTHOR]