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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]

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]

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]

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]

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]