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Surface-dielectric-barrier discharges (SDBDs) can be applied for a wide range of applications, such as ozone generation, surface treatments, and air-pollutants removal. An important advantage of the SDBD plasma is that relatively low high-voltage (HV) pulses (<10 kV) are needed to generate the plasma. They are effective in removing a wide range of pollutants. Despite their high energy efficiency, plasma decomposition generally results in the reaction by-products and the formation of ozone and nitrogen oxides. This drawback can be overcome by combining the SDBD plasma with catalysis. In this paper, a novel plasma-catalytic topology is proposed for the purpose of on-demand air purification. The main idea of the plasma-catalytic reactor is that both the plasma and the catalytic function are configured as planar structures which are positioned in parallel to each other. The plasma is generated along a planar dielectric structure. We use an SDBD for this purpose. Plates coated with the catalytic material are positioned in parallel to the SDBD plates. The air to be treated is flushed along the plates. There are no restrictions to the type or combination of catalysts used; the catalysts and their specifications can be chosen freely. We have developed a modular plasma-catalytic SDBD reactor to handle large flows, which can be scaled up and scaled down easily. To energize the plasma, an SDBD power modulator was developed. The modulator is able to generate a HV output pulse over an SDBD plasma load with a magnitude adjustable from 4.78 to 6.95 kV. The pulse rise time is about $1~\mu \text{s}$ and its ramp is about 6 kV/ $\mu \text{s}$. The energy per pulse then ranges from 1.1 to 17.4 mJ. The output power can be adjusted up to 48 W at a repetition rate of 5.5 kHz. The maximum possible pulse repetition rate is 22 kHz, but it is limited to 5.5 kHz due to the limited current rating of the available dc power supply. The total energy efficiency of the power modulator is 68%. A single modulator unit can power up to two SDBD reactor plates of $100\times 150$ mm size, having plasma at both sides of the plate. The operational efficiency of the developed SDBD catalytic reactor has been investigated by studying the removal of NOx and ethylene. The removal efficiency of NOx and ethylene is determined as a function of energy density and operational parameters, such as their initial concentrations and the gas flow rate. [ABSTRACT FROM AUTHOR]

Water can be activated by applying plasma to water, for instance, by creating plasma inside (bubbles in) the water, or along a water surface. Plasma-activated water (PAW) typically contains hydrogen peroxide, nitrates, nitrites, and peroxynitrite, and typically has a pH ranging from 2 to 4. The components of PAW and the low pH have proven synergistic antimicrobial effects against bacteria, biofilms, yeasts, and other microorganisms. This paper describes a power modulator and a plasma reactor system for high-yield production of PAW at high production rate. A compact and solid-state dual resonant system has been realized and successfully demonstrated for industrial PAW production. The system generates up to 80-kV (theoretical 120 kV is possible) dual-resonant high-voltage pulses with an oscillation frequency up to 2 MHz, pulse repetition rate > 20 kHz, and an average power of 800-W continuous. In addition to the power modulator, the PAW production system consists of a transient arc plasma reactor and a loop system. Depending on the application, the system is able to activate 10–100 L/h. The disinfecting properties of the PAW production system have been verified by experiments on the reduction of Staphylococcus Epidermidis. Directly after its production, the log reduction of S. Epidermidis can be as high as >8 log. During a period of at least 40 min after its production, the PAW has “mild” disinfecting properties, being able to deactivate S. Epidermidis by 3–4.1 log. [ABSTRACT FROM PUBLISHER]

Industrial application of nanosecond pulsed corona technology for air purification requires high volume, high-power plasma reactors. Cylinder-wire type reactors require multiple cylinders to meet these demands. Variations in pulse waveforms per cylinder, misalignment of wires, and jitter in streamer inception could lead to an uneven energy distribution over the cylinders. Nanosecond ICCD imaging is applied to a semi-industrial scale pulsed corona reactor to study streamer inception and propagation of the streamer plasma simultaneously in 16 cylinders. The images show streamer inception of all cylinders within 9 ns. Streamer propagation and intensities are very similar for all cylinders. [ABSTRACT FROM PUBLISHER]

In this paper, we present the final implementation of our 0–50-kV picosecond rise time 0.5–10-ns pulse generator. The pulse generator will be used in future work to generate a (sub)-nanosecond streamer plasma for air purification research. The pulse generator is a single-line pulse generator with an oil spark-gap (SG), which generates 0.5–10-ns pulses with a 200-ps rise time and can operate at repetition rates of over 1 kHz into a 50- \Omega load. It is an improvement over the first implementation of our nanosecond pulse generator that we designed and verified experimentally in previous work. In this paper, we evaluate the performance of the final design. Furthermore, we present 3-D electromagnetic simulations of the nanosecond pulse generator and show that the simulations are in good agreement with the measurements. A variation in pulse duration from 0.5 to 10 ns is possible and the output pulses are square shaped without the large plateau behind the main pulse that was present in the pulses from the first implementation of the nanosecond pulse generator. At high voltages, the pulse top becomes less flat due to a time-dependent mismatch in the spark-gap. Furthermore, investigation of electrode erosion of the oil spark-gap shows that the erosion rate of the electrodes is in the range of 200–600 \mu \mathrmcm^3 \cdot \mathrmC^-1 for the electrode that is mainly the cathode and 100–300 \mu \mathrm{cm}^{3} \cdot \mathrm{C}^{-1}$ for the electrode that is mainly the anode, respectively. This is almost an order of magnitude higher than most gas spark-gap studies show for brass electrodes. Therefore, electrode erosion in the oil spark-gap will be a limiting factor on the lifetime of the system. We designed a new electrode with a stainless steel head to increase this lifetime. [ABSTRACT FROM PUBLISHER]

Fast and repetitive switching in high-power circuits is a challenging task where the ultimate solutions still have to be found. We proposed a new approach. Supercritical fluids (SCFs) combine favorable properties of liquids - insulation strength, thermal behavior, and gases - self healing, high fluidity, and absence of vapor bubbles. That's why we start investigating the subject of plasma switches in SC media. First results indicate excellent switch recovery and very high insulation strength. We present the design of a SCF insulated switch (SC switch). Breakdown strength of the SCF is investigated and found to be high in comparison with most of the solid insulating media. The dielectric recovery inside the SC N2 switch is tested under a repetitive 30 kV, 200 ns pulse voltage at repetition rate up to 5 kHz. The recovery breakdown voltage across the SC switch achieves 80 % within 200 μs. The current interruption capability of SC N2 is investigated experimentally in a synthetic circuit generating a high-frequency arc of several hundreds of amperes and a transient recovery voltage of hundreds of volts. The results show that a SC N2 switch with fixed electrodes and an inter-electrode distance of mm range can successfully interrupt this current at approximately 2 ms after arc initiation. [ABSTRACT FROM PUBLISHER]

By the application of pulsed corona discharges in a carbon dioxide atmosphere over a water film, the formation of methane has been observed under mild reaction conditions, without the application of a dedicated catalyst. Methane is proposed to result from hydrogenation of carbon monoxide and possibly also carbon dioxide at the NiCr alloy high-voltage electrodes, the precursors being formed by plasma-induced decomposition of carbon dioxide and water. Applying energy densities up to 46 kJ/L has yielded methane levels of approximately 440 ppm at a production efficiency of 398 pmol/J. The observed plasma chemistry occurs at ambient pressure, while gas phase heat is cooled away by the water film, the latter being thermally nearly unaffected. [ABSTRACT FROM PUBLISHER]

Matching a pulse source to a plasma load is one of the main challenges to overcome to maximize the full potential of pulsed discharges for air purification applications. In this paper, we propose experiments that investigate the matching of a nanosecond pulse source to a corona plasma reactor that is aided by a high voltage on a tertiary electrode. The corona plasma reactor is a wire-cylinder reactor, as is commonly used in pulsed power plasmas. A tertiary electrode is situated on a dielectric layer against the cylinder of the reactor. On this tertiary electrode, we can apply a pulsed RF or dc voltage to provide an additional plasma and bias voltage in the corona plasma reactor. The pulse source that energizes the main corona plasma is the nanosecond pulse source of Kumamoto University, Japan. In this paper, we show the results of experiments with a dc voltage on the tertiary electrode. We varied the amplitude of the pulsed voltage as well as the dc voltage and investigated their effect on the corona plasma with energy and ozone measurements. The results show that the matching to the reactor increases with increasing dc voltages. However, the matching effect decreases with higher repetition rates. Furthermore, ozone measurements confirmed that a better matching also results in a higher ozone production, but in a lower ozone production energy yield. [ABSTRACT FROM PUBLISHER]

Although pulsed corona technology for air purification is widely investigated by the lab experiments, large-scale application has yet to be proven. Industrial systems require large flow handling and thus, high corona power. An autonomous semi-industrial scale pilot wire-cylinder type corona reactor has been constructed for air purification demonstrations. The reactor is powered by a 10-kW spark gap-based pulsed power supply, capable of generating 60-kV 100-ns wide pulses with 1-kHz repetition rate. The pulses are optionally superimposed on a 0–30-kV dc bias to enable electrostatic precipitation. The system has been successfully applied during several field and lab experiments. Conversion data as a function of energy density are presented for NOx, NH3, H2S, toluene, limonene, and fine dust removal. The system proves feasibility of large-scale air purification by pulsed corona. [ABSTRACT FROM AUTHOR]

In this paper, pulsed-power technology was applied to plasma printing, which is a maskless plasma patterning solution that is being developed for the fabrication process of printed electronics. A high-voltage pulse source was developed and applied to a high-speed plasma printer to improve the speed of plasma printing. Experiments on plasma printing were used to compare the performance of the pulse source with the currently used alternating-current source. From plasma experiments, an electrical plasma model was derived for the plasma printer. Different parameters were investigated, such as the plasma energy as a function of gap distance, applied voltage, and the total amount of plasma that was generated. From these experiments, a connection was made between the plasma energy and the print effectiveness to arrive at optimal parameter values for fast plasma printing. It was concluded that higher plasma energy leads to higher print effectiveness, which leads to an increase in plasma print speed by a factor of 10 when using the pulse source. Moreover, scaling the PlasmaPint technology to reach higher print speeds is achievable by using more print heads or print heads with more tips. [ABSTRACT FROM PUBLISHER]

A spark discharge generated by a 5-ns high-voltage pulse of 21 kV with a rise-time of 200 ps in a 1-mm gap between half-sphere steel electrodes was investigated in N2–O2 gas mixtures at atmospheric pressure. We compared short exposure and long exposure ICCD images of the discharge, as well as single shot images and accumulated images. At high repetition rates more discharge channels form due to higher background ionization. The influence of the O2 concentration between 0.1 and 10 vol% O2 in N2 is insignificant. [ABSTRACT FROM PUBLISHER]

Dielectric barrier discharges generated in a coaxial tip to cylinder configuration at atmospheric pressure by a 5-ns high-voltage pulse with sub-ns rise time were investigated with a fast intensified CCD camera. Different discharge characteristics were found for the breakdown during the pulse itself and in the subsequent reflections of the pulse. There is a transition from a complete diffuse regime to a breakdown in constricted channels, which finally cross the whole gap. [ABSTRACT FROM PUBLISHER]

Surface dielectric barrier discharges (SDBDs) provide homogeneous plasma over a large surface area. This allows surface treatments of foils, textiles, or fibers. In this paper, we present results of a study to characterize the pulsed performance of SDBD by fast imaging of the plasma development. [ABSTRACT FROM AUTHOR]