Ns Pulsed Discharge Research Articles

PIC/MCC simulation for a ns-pulsed glow discharge in nitrogen at sub-atmospheric pressure and analysis of its quasi-steady state physics

The present study investigates the physics of a nanosecond-pulsed microplasma operated at a pressure of 200 mbar with the help of a particle-in-cell simulation with Monte Carlo treatment of collision (PIC/MCC) and (semi-)analytical models. The discharge is ignited in a 1 mm gap between two parallel molybdenum electrodes by applying a voltage in the kV-range for several tens to hundreds of nanoseconds. A PIC/MCC simulation code is developed in order to describe the experiment performed under identical conditions. The simulation includes the external electrical circuit to perform ab-initio calculations of the complete experimental setup. Notable features of the PIC/MCC are (i) the adjustment of super-particle weights to reduce the computational load during drastic changes of the plasma density, which reaches values up to a few , and (ii) the inclusion of dissociative recombination of the ions, which is the key loss process for the charge carriers in the plasma bulk regions. The current and voltage waveforms obtained from the simulation are compared to the experimentally measured ones and good agreement is found. After ignition, the discharge establishes a quasi-steady state exhibiting spatial features similar to a conventional DC glow discharge. Using the PIC/MCC results, reasonable approximations are identified, which allow the development of various analytical fluid models for the individual plasma regions. These models are able to reproduce the key features of the discharge in agreement with the PIC/MCC results. The simplified models for the different discharge regions can be combined to describe the global behaviour of the discharge and—in a next step—might be used to develop computationally efficient global chemistry models that account for the different power dissipation mechanisms along the discharge gap.

Behavioral characteristics of nanosecond pulsed discharge in coaxial electrodes

AbstractThe environmental improvements by pulsed discharge plasma, a type of nonthermal plasma, have received much attention all over the world. The observation of discharge plasmas is beneficial for better understanding of the plasma physics of this growing field. Recently, nanosecond (ns) pulsed discharge with a short pulse duration of 5 ns achieved the higher energy efficiency on ozone generation and NO removal. However, the underlying mechanisms of these high efficiencies remain unclear. In the present study, the effects of electrode geometry on propagation process of ns pulsed discharge in coaxial electrodes were investigated using an ICCD camera. As the results, increasing wire diameters from 0.2 to 2.0 mm lead the different streamer discharge parameters; propagation velocity of streamer heads from 4.8 mm/ns to 12.5 mm/ns, peak of discharge current from 243 to 328 A, respectively. Therefore, it is concluded that the wire diameter is one of the paramount parameters to control the characteristics of the ns pulsed streamer discharge.

Experimental characterization of a ns-pulsed micro-hollow cathode discharge (MHCD) array in a N2/Ar mixture

An array of seven micro-hollow cathode discharges (MHCDs) operating in a N2/Ar mixture and ignited by a nanosecond pulsed high voltage is experimentally characterized in this work. Compared to other non-equilibrium discharges, high electron densities can be obtained with this type of microdischarge, and, thus, a high dissociation degree of the molecules is expected to be achieved. This is particularly suited for nitride deposition, which is the targeted application of this work, given that the atomic nitrogen density is a key parameter for this deposition process. The electrical diagnostics reveal that the energy deposited in the plasma during one voltage pulse increases with the Ar fraction in the gas mixture and the voltage pulse repetition frequency. A small effect of the repetition frequency is observed on the voltage and current characteristics of the discharge, while a significant increase in the amplitude of these two electrical parameters is observed with increasing Ar admixture. Consequently, a higher electron density is expected with increasing Ar fraction in the gas mixture and repetition frequency. Time-integrated optical emission spectroscopy is carried out to identify the excited emissive species in the plasma and to determine the time-averaged vibrational and rotational temperatures. For a discharge operating in pure N2, at a repetition frequency of 40 kHz, the time-averaged rotational temperature is found to be 390 K ± 40 K and the time-averaged vibrational temperature is 3580 K ± 200 K, revealing the non-equilibrium nature of the discharge. Both temperatures increase with the Ar fraction in the N2/Ar mixture, while they are almost independent of the repetition frequency. Finally, the different phases of the spatio-temporal evolution of the discharge are mapped using space-time resolved ICCD images. The spatial evolution of the discharge between two consecutive voltage pulses can be decomposed in four phases, corresponding to the different stages of the temporal evolution of the discharge voltage.

Decomposition of Toluene Using Nanosecond- Pulsed-Discharge Plasma Assisted With Catalysts

Volatile organic compounds (VOCs) are common air pollutants existing in various atmospheric environments; as they present both acute and chronic effects on the health of a number of different human systems and organs, methods for their efficient removal are essential. To this end, catalysis is being researched to prevent environmental pollution. While catalytic and photocatalytic oxidation, which can eliminate low concentrations of various kinds of VOCs as well as O3, offer potential to improve indoor air quality, neither is effective in areas with high VOC concentration. To overcome this limitation, many researchers have concentrated on synergetic effects of plasma catalysis, combining the advantages of high-selectivity catalysis and fast ignition and response of a nonthermal plasma. The authors’ research group has demonstrated that our nanosecond (ns)-pulsed-discharge plasma decomposes NO x as well as produces O3 with an energy efficiency higher than that of the reported nonthermal discharges. However, the performance of the ns-pulsed-discharge plasma in VOC decomposition in comparison with or without catalyst has not yet been investigated systematically. Thus, this paper experimentally clarified the combined effects of MnO x catalyst supported by Ni foam on toluene decomposition. The input energy density to our plasma catalysis reactor using a ns-pulsed discharge was 11% of a cited dielectric barrier discharge plasma catalysis when toluene removal ratio reached 100%.

Energy Efficiency Improvement of Nitric Oxide Treatment Using Nanosecond Pulsed Discharge

Pulsed streamer discharge plasmas, one type of nonthermal plasma, have been used to treat exhaust gases. Since a pulsewidth of applied voltage has a strong influence on the energy efficiency of the removal of pollutants, the development of a short-pulse generator is of paramount importance for practical applications. In this paper, a nanosecond (ns) pulse generator which has a 5-ns pulse duration in output pulsed voltage is developed, and NO-removal experiments using ns pulsed discharge were conducted. The experimental results of the NO removal showed 100% of NO-removal ratio at 7 pps of pulse repetition rate and the extremely high energy efficiency, which is 0.43 mol/kWh (12.9 g-NO/kWh) for NO removal (initial NO concentration = 200 ppm; gas flow = 2.0 l/min ). The result of deriving energy efficiency for NO removal indicated that the ns pulsed discharge has great advantage in energy efficiency for NO removal to the conventional discharge methods. By this research, the utility of the ns pulse plasma process was proven, and the influence of shorter pulse duration on NO-removal energy efficiency was confirmed.

Pulsed Power Technology for Pollution Control

Recently, the pulsed power technology led us to generate discharge plasma in high-pressure gas, liquid and solid environment. The discharge plasmas have a lot of functions such as an intense electric field, a large current flow, a chemically active radical formation, a shockwave generation, and an ultraviolet irradiation. Using the functions, the pollution control technologies, including exhaust gases treatment, ozone generation, water treatment, and material destruction or separation, were developed in laboratory. In the paper, the NO removal by ns pulsed discharge plasma and the aggregate recycling by the discharge inside of concrete would be introduced.