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Atmospheric repetitive He discharge with 10 ns current peak width and 3×1011 V/s voltage front rise working in jet geometry is studied. This part deals with the ionization waves, electron density, and electric field dynamics. The electron density (ne) is measured by Stark broadening of the H Balmer β (Hβ) and He emission lines, the electric field is analyzed using Stark polarization spectroscopy, and the ionization waves are studied by fast imaging. We found that the ionization fronts propagate in the quartz tube with a velocity of about 5×105 m/s; this velocity slowly decreases along the tube but may jump in the open air at some conditions. In the space between electrodes, ne increases rapidly at the beginning, reaching about 7×1015 cm−3, which corresponds to electron avalanche defining the discharge current peak. In the tube, the electrons are concentrated in the ionization wavefronts having low density (

This study proposes an improved high-voltage fast impulse generator based on an inductive energy storage system with a 4 kV static induction thyristor. Nanosecond-scale impulses with pulse widths below 100 ns and a peak voltage of up to 15 kV can be generated by modifying the high-voltage transformer in the circuit and tuning the circuit capacitor. The resulting device is highly stable and can perform continuously if the discharge parameters are chosen within the recommended range. A plasma jet was operated using the generator at low temperature (below 37 °C). Together with its high stability and potential for continuous operation, the proposed generator offers promise for use in biomedical and agricultural applications. Furthermore, the nanosecond-scale high-voltage impulses produced by the generator enable it to achieve an electron density in the plasma one order of magnitude higher than the commercially available radio frequency plasma jet analog. We also show how to reduce the total cost of the generator.

Atmospheric repetitive He discharge with 10 ns current peak width and 3 × 10 11 V s−1 voltage front rise working in jet geometry is studied. The first part of the study is devoted to electrical and optical discharge characterization including voltage-current behavior, emission dynamics, as well as ro-vibrational dynamics of N2, N 2 + and OH molecules. It is found that He atoms get excited at the very early stage, as a result of ionization wave formation. This process follows by excitation of O, N2 and N 2 + . It is also shown that a rather small (0.1%–1%) air admixtures facilitate gas breakdown, as revealed by shortening of the discharge current risetime. The rotational excitation of N 2 + always overtakes He excitation by about 5 ns, with rotational temperature peaking at about 650 K and decaying afterwards, whereas rotational temperature of N2 always remains constant equal to about 300 K. This value is associated with gas kinetic temperature since the electron-rotational (e-R) excitation process is too slow, so it cannot be activated during the plasma phase and no additional change in rotational excitation of N2 happens. Nitrogen molecules remain vibrationally excited in the discharge, post-discharge and jet areas after the plasma pulse which is likely a result of ionization wave propagation. Upon water vapor injection the apparent OH rotational distributions reveal double Boltzmann slope representing thermalized and non-thermalized OH groups. Rotational temperature of the thermalized group correlates with the one of N 2 + showing, however, much longer relaxation time, whereas for the non-thermalized group it remains above 1 eV at all conditions. The obtained results confirm that the studied ns- discharge is a good candidate for temperature-sensitive applications, such as the bio-sample treatment. Further analysis related to the ionization waves, electron density and electric field behavior is undertaken in the second part.

Re-pulsing glow discharges in gaps up to 2 cm were experimentally investigated in atmospheric pressure air. Discharge was ignited as a sequence of spark and glow discharge and sustained in a glow regime after ignition. It was confirmed that the discharge with defined parameters could be ignited without any adjustments after initiation of the discharge. The discharges were characterized by a high-speed camera, current and voltage measurements, and optical emission spectrometry (OES). Typical structure of the glow discharge consisting of cathode glow, dark faraday space, positive column, and anode glow was observed. Transition from subnormal to normal glow mode was confirmed by analysis of current and voltage waveforms. It was found by OES that the type of discharge strongly affects the ratio of produced reactive species. It was confirmed that with change of discharge from subnormal to normal glow regime, rotational temperature could vary across a wide range (from 1650 to 3500 K). The developed device allows glow discharge to be ignited with defined parameters, which makes the control of the gas temperature and ratio of reactive species possible by presetting the discharge parameters. Additionally, it was demonstrated that corona discharge or repeating spark discharges could also be generated using the developed device without additional manipulations of the experimental setup by adjusting the discharge parameters.

BackgroundVanillin is the main byproduct of alkaline-pretreated lignocellulosic biomass during the process of fermentable-sugar production and a potent inhibitor of ethanol production by yeast. Yeast cells are usually exposed to vanillin during the industrial production of bioethanol from lignocellulosic biomass. Therefore, vanillin toxicity represents a major barrier to reducing the cost of bioethanol production.ResultsIn this study, we analysed the effects of oxygen-radical treatment on vanillin molecules. Our results showed that vanillin was converted to vanillic acid, protocatechuic aldehyde, protocatechuic acid, methoxyhydroquinone, 3,4-dihydroxy-5-methoxybenzaldehyde, trihydroxy-5-methoxybenzene, and their respective ring-cleaved products, which displayed decreased toxicity relative to vanillin and resulted in reduced vanillin-specific toxicity to yeast during ethanol fermentation. Additionally, after a 16-h incubation, the ethanol concentration in oxygen-radical-treated vanillin solution was 7.0-fold greater than that from non-treated solution, with similar results observed using alkaline-pretreated rice straw slurry with oxygen-radical treatment.ConclusionsThis study analysed the effects of oxygen-radical treatment on vanillin molecules in the alkaline-pretreated rice straw slurry, thereby finding that this treatment converted vanillin to its derivatives, resulting in reduced vanillin toxicity to yeast during ethanol fermentation. These findings suggest that a combination of chemical and oxygen-radical treatment improved ethanol production using yeast cells, and that oxygen-radical treatment of plant biomass offers great promise for further improvements in bioethanol-production processes.

Re-pulsing glow discharges in atmospheric-pressure air were experimentally investigated using a push-pull generator with pulse-width modulation. Discharges were ignited as a spark-glow discharge sequence and sustained in a glow regime after ignition in a gap of 2 cm and characterized by current and voltage measurements, as well as by optical emission spectroscopy. It was found that at a certain range of parameters, the discharge could be stabilized even in the presence of external airflow. It was demonstrated that the type of discharge and total power dissipated in the plasma volume could be precisely controlled by pulse-width modulation. Additionally, it was confirmed that the rotational temperature varied across a wide range (1640-2440 K) by using pulse-width modulation with gas-flow control, when vibrational temperature was around 4610 ± 770 K. The generation of stable glow discharge in the presence of gas flow with a wide range of parameters that could be precisely controlled by pulse-width modulation looks promising for use in energy-efficient gas conversion.

Recently, marine resources have been attracting much attention owing to their growing role in sustainable development. Growing interest in the exploration of marine resources and numerous studies on ecology and biochemistry has made the high-precision analysis of sea water necessary. In this paper, the possibility of using the atomic emission spectroscopy of microarc discharges generated in sea water for on-site contaminants detection and elemental composition analysis has been studied. We analyzed the discharge process and optical emission spectra from microarc discharges in three types of liquid, namely, artificial sea water composed of ten main components, reference solutions containing a single component each, and naturally sampled deep sea water. Microarc discharges were generated under low breakdown voltages using a compact experimental setup with a needle-to-plate electrode system immersed in each liquid in a quartz cuvette. In the spectra, the emission peaks of the main components of sea water and contaminants from the electrodes were detected, and reference solutions were used for the identification of unassigned peaks. To study the effect of electrode materials on the optical emission spectra and plasma parameters, three types of needle electrodes were used. The effect of the experimental conditions on the measured optical emission spectra was studied, and the applicability of proposed method for on-site detection of metals and elemental composition analysis was confirmed.

For low-temperature atmospheric pressure plasma treatment applications, we developed a novel rotating arc jet operated using various gases, including ambient air. We demonstrate the operation of plasma via the injection of various gas mixtures and tune operation parameters to achieve a low-temperature gas output from the arc jet. The rotating arc jet has an efficiency two orders of magnitude higher in the generation of reactive oxygen and nitrogen species than commercially available conventional nonequilibrium atmospheric pressure plasma jets operated with He or Ar gases. The high concentration of reactive species and use of ambient air as a process gas is promising for biomedical and agriculture applications. This work is a step toward the commercial use of plasma jets operated with ambient air.

We report a very low energy cost for NO radical formation found in atmospheric spark discharge. For this purpose non-equilibrium air discharges working in spark and glow regimes were studied showing the optimum performance in the vicinity of the spark-to-glow transition. The minimum energy cost for NO production of about 80 eV/molecule (calculated based on the total direct current power applied to the discharge) is achieved in the spark regime before the transition, whereas the maximum NO yield (of about 10^4 part per million) corresponds to the glow regime. Based on the estimated power absorbed in plasma the energy cost below 4 eV/molecule is achievable in the spark regime, which is close to the Zeldovich reaction enthalpy of NO formation (about 3 eV/molecule). The result implies that the energetic effciency of a single spark may exceed that of the modern Haber-Bosch cycle (with energy cost of about 5 eV/molecule in the case of ammonia, according to Patil et al., Catalysis Today, 256 (2015) 49). The found low energy cost is associated with the discharge non-equilibrium caused by short spark duration.

Microplasma discharge in sea water was investigated using a needle-to-plane electrode system with various types of needle insulation. A platinum plane electrode and a palladium needle electrode were placed with a gap of 20 $\mu \text{m}$ in the artificial sea water. A pulse current source, consisting of a MOSFET switch, a capacitance, and inductance, was used. The sea water between the electrodes performed as resistance for the current source circuit. Using the microgap configuration, microplasma discharges were reproducibly ignited under low breakdown voltages in the highly conductive sea water. In order to significantly diminish the current dispersing into the surrounding water, the needle electrode was insulated, enabling more accurate investigation of the preheating and bubble formation processes before the microplasma discharge. It was established that the microplasma discharge was ignited after formation of the bubble of size, sufficient to cover entire discharge gap between the electrodes. Influence of the needle electrode insulation on microplasma parameters was investigated.

In this work, we developed a portable device with low production and operation costs for generating ambient-air glow discharge (AAGD) that is transferred to the surface of flowing liquid and demonstrated its applicability to practical use in agriculture. An experiment procedure that ensured the stable treatment of various liquids was established. Additionally, it was found that humidity did not have a significant effect on the treatment process, which makes the use of the developed device possible in various locations. It was found that an L-phenylalanine solution treated with AAGD allows simultaneous 40% hydroponic radish-sprout growth promotion with a bactericidal effect. Further, scalability and practical-application possibilities in hydroponic plant growth were discussed.

In this work, micro-arc discharge is investigated using a needle-to-plane electrode system placed with a micro-gap in highly conductive artificial seawater. A major problem with microarc discharge is the erosion of electrodes caused by the high current of the arc, however, it was found that erosion of the needle electrode did not have any effect on the discharge process in the case of precise control of the discharge gap. A simple mathematical model was developed for a more detailed study of the preheating phase of the discharge. The modeling showed good agreement with the experimental results and confirmed that the needle electrode could be reused to generate reproducible micro-arc discharges even after the erosion caused by the arc. Moreover, it was found that, in certain conditions, the preheating phase could be simulated using a simple inductor-capacitor-resistor (LCR) oscillator model with a resistor instead of electrodes immersed in the liquid. It was confirmed that the shape of the needle electrode&rsquo, s tip did not affect the measurement of optical emission spectra in the case of precise focusing, which could be used in the development of compact analytical tools for on-site analysis of deep-sea water using atomic emission spectroscopy.

Nanocrystalline ZnO films were deposited by rf reactive magnetron sputtering. The films were characterized by reflection high-energy electron diffraction, X-ray photoelectron spectroscopy and gas sensing measurements. It was found that annealing of the film enabled to invert its conductivity type. Thus, as-deposited ZnO film showed p-type conductivity while annealed film showed n-type conductivity behavior. The p-and n-type conductivities of the films obtained by gas sensing measurements have been confirmed by XPS results. The gas sensing properties of the films were investigated upon exposure to 10 ppm of NO2at 22°C and exhibited good sensitivity with fast response and recovery times. The sensor response to NO2was found to be profoundly dependent on the conductivity behavior of the film.

Micro-arc discharge plasma was generated in highly conductive seawater at high pressures up to 19 MPa. Using a microscaled rod-to-rod electrode system, a micro-arc discharge was ignited reproducibly using voltages below 850 V. Even at high pressure, the current and voltage characteristics showed the same scheme of micro-arc discharges as those at atmospheric pressure. The energy consumption for the preheating phase, in which bubbles were generated by joule heating and micro-arc discharges were consequently ignited in the bubbles, gradually increased from 5 to 36 mJ with an increase in pressure from 0.1 to 19 MPa. The micro-arc discharge plasma at high pressure exhibited high-luminance photo-emissions with distinctive spectra consisting of an intense flat continuum band and extremely broadened peaks.Micro-arc discharge plasma was generated in highly conductive seawater at high pressures up to 19 MPa. Using a microscaled rod-to-rod electrode system, a micro-arc discharge was ignited reproducibly using voltages below 850 V. Even at high pressure, the current and voltage characteristics showed the same scheme of micro-arc discharges as those at atmospheric pressure. The energy consumption for the preheating phase, in which bubbles were generated by joule heating and micro-arc discharges were consequently ignited in the bubbles, gradually increased from 5 to 36 mJ with an increase in pressure from 0.1 to 19 MPa. The micro-arc discharge plasma at high pressure exhibited high-luminance photo-emissions with distinctive spectra consisting of an intense flat continuum band and extremely broadened peaks.

Microplasma discharge in sea water for optical emission spectroscopy was investigated using a needle-to-plane electrode system. The electrodes of a Pd needle and a Pt plate were placed with a gap of 25 µm in typical artificial sea water or locally sampled natural deep sea water. A pulse current source, consisting of a MOSFET switch, a capacitor, an inductor and the resistance of the sea water between the electrodes, was used. The circuit parameters were optimized to decrease the breakdown voltage and the spark duration to suppress erosion of the electrodes. Using a microgap configuration, spark discharges were reproducibly ignited in the highly conductive sea water at low breakdown voltages. The ignition of spark discharges required not only a critical voltage sufficient for breakdown, but also a critical energy for preheating of the sea water, sufficient for bubble formation. The possibility of using optical emission spectroscopy of microplasma in water is shown for identifying elemental composition of sea water.