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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]

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. [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]

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]

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]

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]