Pulsed Positive Corona Research Articles

Evolution of streamer groups and radical generation in high-voltage multiple-pulse-induced nonthermal plasma

Nonthermal plasmas (NTPs) induced by atmospheric nanosecond multiple-pulse corona discharge have been studied to control pollution generated by combustors, such as boilers, incinerators, and diesel engines. In high-speed short-width high-voltage pulsed corona discharge-induced plasmas, the chemical reactions that occur between multiple pulses and the characteristics of the electron density (denoted by ne) and ozone during the second pulse have not been fully clarified. In this study, we perform quasi-two-dimensional numerical analysis of nonequilibrium NTP induced by a nanosecond positive pulsed corona discharge. The continuum fluid equations for a two-temperature nonequilibrium NTP are used as governing equations. A total of 197 gas phase reactions for 25 chemical species and 21 surface reactions on the inner glass wall surface are considered in an air plasma under atmospheric pressure. We simulate streamer group behavior up to the second pulse and found that ne and the length of streamers change due to chemical reactions between pulses. In addition, we successfully simulated the phenomena of ne reduction and streamer suppression that occur primarily during the second pulse. This is caused by the decrease in potential gradient due to the space and dielectric surface charge build-up. Furthermore, it is confirmed that the ozone formation reaction mainly occurs between pulses. This simulation enables predictions of phenomena in nanosecond positive multiple-pulse plasma systems.

Experimental mapping of the ozone distribution in a pulsed positive corona discharge to estimate the efficiency of ozone production

The spatial and temporal evolution of the ozone density has been measured in a 1 cm electrode gap tip to plane positive pulsed corona discharge in air at atmospheric pressure with no gas flow. It was expected to observe a higher ozone density in the vicinity of the discharge gap but ozone has been found at a quasi uniform density level up to 10 cm from the electrode gap after only 30 s of ignition. Such a wide distribution of ozone in the reactor cell is attributed to strong turbulence mostly triggered by the ionic wind. The mapping of the ozone density associated to the power measurement led to the estimation of the ozone production yield in term of mass per electrical energy.

Efficacy of cold atmospheric plasma for inactivation of viruses on raspberries

In this study, the effectiveness of cold atmospheric plasma (CAP) in inactivating murine norovirus (MNV/human norovirus surrogate) and hepatitis A virus (HAV) on aerosol-inoculated dark red Willamette raspberries was explored. Pulsed positive corona discharge system fed by synthetic air was used for the production of CAP. Raspberries were treated for 1, 3, 5, 7, and 10 min at 25 W. Application of CAP enabled a 4 log10 infectivity reduction in <5 min for MNV and approximately 10 min for HAV (from starting level of 6.91 and 7.84 log10 PFU/mL, respectively). Viral genome copies reduction of 3.18 log10 for MNV and 4.32 for HAV were found from starting level of 5.76 and 6.47 log10 gc/μL, respectively. CAP treatment did not result in significant degradation of fruit color, an important quality attribute. The study demonstrated CAP as an efficient post-harvest decontamination method to reduce viral load in raspberries without significantly affecting its quality parameters. Industrial relevanceDue to the fast-processing paces required in the raspberry industry, it is difficult to assure the complete microbiological safety of this fruit. Cold atmospheric plasma is a practical, environmentally-friendly, non-thermal tool for the effective reduction of microbial pathogens. The model developed in this study demonstrated that CAP treatment of fresh raspberries not only inactivated hazardous enteric viruses in a short time (10 min) but also unaffected fruit color stability. The simplicity of described CAP design and low-cost inputs (air and electricity) enable the commercial application of inexpensive plasma chambers for continuous surface decontamination of large volumes of raspberries without bringing processing to a standstill.

Indigo Carmine Degradation in Water Induced by a Pulsed Positive Corona Discharge in Air: Discharge and Postdischarge Effects

In recent years, one of the fastest growing technological applications in the field of nonthermal plasmas is the degradation of organic contaminants of water. In this work, the degradation of indigo carmine (IC) in water induced by a pulsed positive corona discharge operating in ambient air is reported. Degradation levels in different volumes of IC in solution with distilled water treated with different plasma exposure times immediately after discharge (0 h), and in the postdischarge up to 24 h were examined. To explain the IC discoloration in the postdischarge phase, a chemical model was developed. The stability of the reactive species in solution nitrate (NO3−), nitrite (NO2−) and hydrogen peroxide (H2O2), as well as the properties of the solution (electrical conductivity, pH) were also measured. The results suggest that the hydroxyl radical (OH˙) as well as ozone (O3) are the main oxidizing species during the discharge phase, being primarily formed in the gas phase through plasma-mediated reactions and then transferred to the liquid by diffusion, while the OH˙ production in the bulk liquid through the decomposition of peroxinitrous acid (O=NOOH) plays a major role in the IC degradation during the postdischarge. These results are associated with a noticeably increase in the energy-yield values observed at 24 h post-treatment.

Воздействие импульсного тлеющего разряда атмосферного давления на алюминиевые пленки нанометровой толщины

The effect of a positive pulsed corona discharge on the thin-film cathode surface was studied in atmospheric pressure air gaps of 2–8 mm at voltages of 5–15 kV. Observed current pulses had the following parameters: repetition rate about 10-15 kHz, pulse duration of 300-500 ns, and amplitude of 10-20 mA. It was shown that at relatively low average currents of 20–50 μA, the discharge transforms into the glow one near the cathode. Due to the discharge channel radial contraction to micrometer scale, Joule heating of the formed cathode layer can lead to a temperature increase up to 1000 K and cause local erosion of the cathode surface. This mechanism should be taken into account when analyzing the interaction of discharge plasma with biological objects.

Temporal-spatial distribution of [formula omitted] metastable molecules in the pulsed positive streamer in the needle-to-plate gap in sub-atmospheric pressure nitrogen

The morphology of pulsed positive streamer corona discharge, such as the channel shape and branching, depends on the operating gas and its pressure. The streamer morphology in the gases containing nitrogen is usually visualized by the optical imaging based on the optical emission spectroscopy (OES) of N2(C3Πu) and N2(B3Πg) states (2nd positive and 1st positive N2 system, respectively). The OES can also be employed for determining the concentrations of N2 molecules in those short-lived radiative states. However, the conventional OES is of the restricted use for the diagnostics of N2 molecules in long-lived metastable states, e.g. for monitoring the N2(A3∑u+) metastable molecules, which play an important role in the collisional-radiative processes in electric discharges in the nitrogen containing atmosphere. Since the knowledge of temporal-spatial concentration and distribution of N2(A3∑u+) metastable species is important for describing the behavior of the pulsed positive streamer corona discharge, therefore, in this experiment we employed also a laser-induced fluorescence (LIF) technique to investigate behavior of the N2(A3∑u+) molecules formed by the streamer. Both diagnostics, OES and LIF used in this experiment for investigating the pulsed positive streamer corona discharge were performed under various pressures of nitrogen. Owing to the use of the 2-stage MPC ICCD camera in our experiment, the investigation provided the first LIF imaging of the temporal-spatial distribution of N2(A3∑u+) metastable molecules in the pulsed positive corona streamer in the needle-to-plate electrode gap in nitrogen at sub-atmospheric pressures. The time-dependent LIF images enabled estimating the N2(A3∑u+) metastable number density (3 × 1014 cm−3) in the pulsed positive streamer discharge at nitrogen pressure of 30 kPa.

Enhancement of positive pulsed corona by dielectric enclosure

In this work, the effect of positive pulsed corona enhancement by introducing Teflon dielectric enclosure in vicinity to the electrode assembly was studied. The discharge operating in air without the dielectric was able to operate within a very narrow voltage range of approximately 200 V. The pulsing frequency was below 1.2 kHz and current peaks were below 14 mA. Increasing the applied voltage onto the positive electrode beyond this range would result in sparks between the electrodes. When the Teflon tube enclosure surrounding the high voltage electrode was used, the window of stable pulsed corona operation expanded up to 3-5 kV. The pulsing frequency increased up to 12 kHz and the current peak level increased to approximately 35 mA. Increasing voltage beyond the point with peak pulsing frequency would result in a drop of pulsing frequency until the discharge pulsations stopped completely. The Teflon enclosure was able to enhance the average power deposited into the discharge from 10 to 220 mWatt. In addition, the product gases of the enhanced pulsed corona were tested to be mostly ozone with traceable amount of NO2. The discharge used about 150 eV and 1950 eV per one ozone molecule and nitrogen dioxide molecule respectively. The reported here plasma source is promising from the power density/compactness standpoint since significant enhancement (&amp;gt;20 times) of the energy deposition to the discharge can be achieved compared to that of conventional positive pulsed corona.

Generation of reactive atomic species of positive pulsed corona discharges in wetted atmospheric flows of nitrogen and oxygen

The emission spectra of excited radicals (OH (A2Σ), O (3p5 P), Hα (3P)) and emissive species ( N2 (C3Πu)) produced by positive pulsed high-voltage needle-plane corona discharges in atmospheric N2 and O2 flows wetted with 10% H2O at 80 °C are used to investigate the relative concentrations of the produced radicals. The results indicate that the tendencies of the concentrations of radicals with discharge conditions are similar to each other due to their similar excitation processes by electron collision. The influence of oxygen flow mixed with the nitrogen flow on the emission intensities of O (3p5P → ), Hα (3P → 2S), ( 0-0), and N2 (C3Πu → B3Πg 1-0) is presented. When the flow rate of oxygen addition is varied from 0–30 ml min−1, the emission intensities of O (3p5P → ), Hα (3P → 2s), and ( 0-0) increase and reach a maximum. Then, if the oxygen flow rate increases further, the emission intensities tend to decrease. However, the intensity of N2 (C3Πu → B3Πg 1-0) decreases monotonously with the increasing oxygen flow, which indicates that the electron density decreases with the increasing oxygen flow. By the tendencies of the relative intensities to N2 (C3Πu → B3Πg 1-0), the concentrations of the total produced O, H, and are shown to increase with the oxygen flow. Based on the reactions for the production of H and O without and with the addition of O2, the analytic solutions for H and O production are derived in accordance with the experimental results.

Evolution of streamer groups in nonthermal plasma

Nonthermal plasmas (NTPs) induced by atmospheric nanosecond pulsed corona discharge have been studied for controlling pollution from combustors, such as boilers, incinerators, and diesel engines. In high-speed short-width high-voltage pulsed corona discharge-induced plasmas, primary streamer evolution is followed by secondary streamer evolution. Though this phenomenon is known experimentally, the details of the structures of the streamers and their evolution mechanisms have not been fully clarified. In this letter, we perform quasi two-dimensional numerical analysis of nonequilibrium NTP induced by a nanosecond positive pulsed corona discharge. The continuum fluid equations for two-temperature nonequilibrium NTP are used as governing equations. In this study, 197 gas phase reactions for 25 chemical species and 21 surface reactions on the inner glass wall surface are considered in an air plasma under atmospheric pressure. The simulated behavior of the streamer groups agrees with experimental observations. Soon after the voltage increases on the reactor, primary streamers are formed, which may transit the complete gap, disappearing near the peak voltage. Next, second streamers appear, disappearing at the end of the applied voltage pulse. The streamer wavelength and the distance between the streamers in the axial direction are determined. Moreover, ozone generation is shown to be more significant in the secondary streamer. This simulation will allow better predictions for nanosecond positive pulsed plasma systems.

Energy Injected in Multi-tip Pulsed Corona Discharge Reactor in Air at Atmospheric Pressure for Pollution Control

This work is devoted to the analysis of experimental and calculated results obtained in dry air at atmospheric pressure in positive pulsed multi-tip corona discharges. The maximum corona current is analysed as a function of several parameters such as the gap distance, the applied voltage and the anodic tip number. The energy injected in the discharge is also calculated as a function of the above parameters for to optimize the most efficient configuration for the pollution control. Also, the average propagation velocity is discussed as a function of the same operating parameters (gap distance, applied voltage and anodic tip number). Intensified Charged-coupled device pictures are shown to prop up the results obtained in this study.

Comparison of point-to-plane corona in different gases

The point-to-plane DC corona discharges at atmosphere pressure have been investigated experimentally in different gases including argon, helium, N2, O2 and air in a needle-to-plate configuration. The breakdown voltage (the onset voltage of corona and the inception voltage to spark), current-voltage characteristics and the corona images have been measured in the gases under positive and negative polarity. Generally, the breakdown voltage of the positive corona is higher than the negative in the gases except O2 in which the results is reversed. The current of the negative corona discharge is much higher than the positive in all gases. There exists a stable negative corona glow in the gases except air or O2 before the spark occurs, while the pulsed positive corona will transit into the spark directly when the voltage increases, without the stable glow stage.

Pulsed corona discharge driven by Marx generator: Diagnostics and optimization for NOx treatment

A compact, repetitive Marx generator with an external trigger is constructed and coupled with a wire-to-plate corona reactor for a positive pulsed corona discharge studies. The reactor resistance and capacitance behavior during the pulse was observed. It was found that the reactor's capacitance increases three times during the pulse due to the streamer propagation from anode to grounded electrode. Using the time development of the capacitance and resistance during the pulse and the reactor inter-electrode distance, the streamer velocity has been calculated to be 1 × 106 m/s, for system arrangement presented in this work. As an indicator of chemical activity of pulsed corona, ozone production was measured. Emission spectroscopy measurements in the UV region were performed to detect species that appear in the discharge and to determine vibrational and rotational temperatures, which are found to be 3200 K and 340 K respectively. As a measure of pollution control potential of the constructed pulsed corona system, NO oxidation efficiency was investigated and compared with results presented in literature. It was shown that pulsed corona systems with significantly longer pulse durations are competitive with several times shorter pulse duration systems, which implies that chemical efficiency of secondary streamers is comparable with efficiency of primary streamers.

Production mechanism of atomic nitrogen in atmospheric pressure pulsed corona discharge measured using two-photon absorption laser-induced fluorescence

To study the production mechanism of atomic nitrogen, the temporal profile and spatial distribution of atomic nitrogen are measured in atmospheric pressure pulsed positive corona discharge using two-photon absorption laser-induced fluorescence. The absolute atomic nitrogen density in the streamer filaments is estimated from decay rate of atomic nitrogen in N2 discharge. The results indicate that the absolute atomic nitrogen density is approximately constant against discharge energy. When the discharge voltage is 21.5 kV, production yield of atomic nitrogen produced by an N2 discharge pulse is estimated to be 2.9 − 9.8 × 1013 atoms and the energy efficiency of atomic nitrogen production is estimated to be about 1.8 − 6.1 × 1016 atoms/J. The energy efficiency of atomic nitrogen production in N2 discharge is constant against the discharge energy, while that in N2/O2 discharge increases with discharge energy. In the N2/O2 discharge, two-step process of N2 dissociation plays significant role for atomic nitrogen production.

Study of Geometry Structure on a Wire–Plate Pulsed Corona Discharge Reactor

The wire-plate pulsed corona discharge reactor has been regarded as the plasma reactor with highest efficiency for controlling pollutants such as NO and SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in flue gas with high-voltage and short-duration positive pulsed corona discharge. A laboratory-scale pulsed corona discharge reactor with wire-plate electrode configuration is established for optimizing the geometry structure of the wire-plate plasma reactor. In this paper, three different methods are used to optimize the wire-to-wire distance and wire-to-plate distance of the plasma reactor. There are experiments with different conditions including various electrical parameters, streamer parameters, and NO oxidation efficiency. The same results are obtained from all the three experiments. The results indicate that short wire-to-plate distance should be adopted to increase the input energy of the plasma reactor but not too short to cause spark discharge in the reactor. Moreover, the wire-to-wire distance should be at least twice as large as wire-to-plate distance, to reduce the interferences between adjacent wire electrodes.

Effect of pulse width on the production of radicals and excited species in a pulsed positive corona discharge

The effect of pulse width on the production of various radicals and excited species (OH, O, O3, , , OH(A 2Σ), O2(v)) in a pulsed positive corona discharge is measured. The densities of these species are measured using laser-induced fluorescence, light absorption and optical emission spectroscopy. It is shown that the pulsed corona discharge can be divided into three phases related to the production of radicals and excited species: (i) primary streamer, (ii) earlier part of secondary streamer and (iii) later part of secondary streamer. It is shown that phase (iii) is inefficient for the production of most of the radicals and excited species. Therefore, a short pulse is desirable for efficient production of radicals and excited species to cut off the inefficient later part of the secondary streamer.

Streamer Propagation of Positive and Negative Pulsed Corona Discharges in Air

Streamer propagation of positive and negative pulsed corona discharges is observed using streak and ICCD cameras. The discharge occurs in a 13-mm point-to-plane gap in dry air. In the positive discharge, the primary streamer propagates from the point to the plane, and then, the secondary streamer develops from the point to the middle of the gap. When the voltage is high, a midgap streamer is also observed. In the negative discharge, the primary streamer develops from the point to the plane, and then, an anodic channel develops from the plane to the middle of the gap. The velocity and luminous intensity of the primary streamer in the positive discharge increase as the streamer propagates from the point to the plane, while those in the negative discharge show an opposite tendency.

Density and temperature measurement of OH radicals in atmospheric-pressure pulsed corona discharge in humid air

Plasma application for environmental improvement is desirable, and it is worthwhile to clarify the behavior of OH radicals in nonthermal plasma. Under atmospheric-pressure humid air, the time evolutions and spatial distribution of relative density and rotational temperature of OH radicals are measured in pulsed positive corona discharge using laser-induced fluorescence with a tunable optical parametric oscillator laser. The density of OH radicals generated by discharge when 28 kV is applied is estimated to be about 1×1015cm-3 at 3 μs after discharge. The OH density increases with humidity. The rotational temperature rises after discharge. The rate of temperature rise increases with humidity. This phenomenon arises from fast vibration-to-translation energy relaxation of H2O. The spatial distributions of OH rotational temperature indicate that the temperature rises in the secondary streamer channel.

Measurement of N2(A3.SIGMA.+u), N and NO under Atmospheric-Pressure Pulsed Positive Corona Discharge Using Laser-Induced Fluorescence

Density and temporal behavior of N2(A3Σ+u) metastable, N atom, and NO molecule are measured in pulsed positive corona discharge using time-resolved laser-induced fluorescence (LIF) under atmospheric pressure. In N2 discharge, the N2(A3Σ+u) density is independent of discharge voltage V, while the number of N2(A3Σ+u) molecules produced by the discharge increases with V because the thickness of the streamer increases with V. The absolute densities of N2(A3Σ+u) and N are measured using the decay rate of their densities after discharge by recombination reaction. In N2/O2(2%) discharge, the N density decreases after discharge, while the NO density is approximately constant after discharge because NO production reaction N + O2 → NO + O and its decomposition reaction N + NO → N2 + O are equilibrated. In N2/NO(250 ppm) discharge, it is shown that NO in the streamer is rapidly removed by N atoms within 3μs after discharge, then NO outside the streamer is slowly removed by diffused N atoms.

Measurement of Atomic Nitrogen in N2 Pulsed Positive Corona Discharge Using Two-Photon Absorption Laser-Induced Fluorescence

The density and temporal behavior of atomic nitrogen are measured in atmospheric-pressure N2 pulsed positive corona discharge using two-photon absorption laser-induced fluorescence (TALIF). The discharge occurs in a 12 mm point-to-plane gap with 21.5 kV applied voltage. The N density near the tip of the point electrode is approximately 500 ppm immediately after the discharge pulse. It decreases by 40% in a postdischarge period of 300 µs owing to diffusion and recombination reaction.

Measurement of metastable in N2 pulsed positive corona discharge with trace amounts of additives

The density of metastable is measured in various gases (N2/O2, N2/NO, N2/NO2, N2/H2O, N2/CO) after pulsed positive corona discharge using time-resolved laser-induced fluorescence (LIF) under atmospheric pressure. The density in N2/O2(0.25%) is uniformly distributed along the axis of the discharge gap (point-to-plane, 12 mm). This result indicates that is mostly generated in the primary streamer channels. The absolute density is measured by calibrating the LIF signal intensity. When the discharge voltage is 21.5 kV, the density immediately after the discharge pulse is estimated to be (2–3) × 1013 cm−3. The reaction rate constants of with O2, NO, NO2, H2O and CO are roughly estimated using the decay rate of density after the discharge pulse, and are compared with reference values. production is increased approximately twofold when hundreds of ppm of O2, NO or NO2 molecules are added to N2.