Discharge In Atmospheric Pressure Air Research Articles

Electric field measurement in DC corona discharge in atmospheric pressure air using E-FISHG and laser-triggering methods

Electric field measurement using electric-field-induced second-harmonic generation (E-FISHG) draws attention because of its non-invasiveness and is increasingly being applied to various discharge plasmas. However, measurement accuracy of previous studies is unclear since approximations in calibration are inadequate. Therefore, we have developed a measurement and analysis method that does not require approximations and can furthermore obtain the distribution of the electric field. To demonstrate the applicability of the proposed method to discharge plasmas, in this paper, we measure the electric field as a result of the space charge generated by DC corona discharge in atmospheric pressure air and validate the results by comparing them with those obtained using the laser-triggering method. We demonstrate that the electrostatic field and electric field resulting from the space charge can be measured with a difference of about 10% between the results obtained from the laser triggering method and E-FISHG method. The proposed method holds potential for applications in discharge plasmas.

Effects of the ground-electrode temperature on electrical and optical characteristics of a coaxial dielectric barrier discharge in atmospheric pressure air

The applied power and electron energy are believed to play important roles in plasma applications, which can be significantly altered by controlling the ground-electrode temperature in a coaxial dielectric barrier discharge (DBD). The effects of the ground-electrode temperature on the electrical and optical characteristics of the DBD were investigated in atmospheric pressure air. The results show that the breakdown voltage decreases, and the number of discharge pulses, the transferred charges, and the applied power increase with the electrode temperature, while the peak current tends to decrease when the electrode temperature is below −35 °C and above 25 °C, respectively. When the electrode temperature remains constant, the breakdown voltage increases and the applied power decreases with the gap distance. The applied power increases with the applied voltage. The dielectric capacitance, the total capacitance, and the gap capacitance at the electrode temperature below −35 °C are generally higher than those at the electrode temperature above 25 °C. Moreover, they change in the same trend when the electrode temperature and the applied voltage increase. The dielectric and total capacitances increase while the gap capacitance decreases. The relative intensities of the spectral lines increase with the electrode temperature. The electron, vibrational, and rotational temperatures increase with the electrode temperature above 25 °C. However, the electron and vibrational temperatures increase and decrease with the electrode temperature below −35 °C. The secondary emission coefficients and electron energy distributions with the electrode temperature were discussed.

The critical effect of electron acceleration under enhanced electric field near cathode on the formation of runaway electrons and diffuse discharge in atmosphere

Runaway electrons (RAEs) are believed to affect the dynamics of ultra-fast gas breakdown significantly. In this work, considering the field enhancement effect near the micro-protrusion on the cathode surface, the formation of RAEs and diffuse discharge in atmospheric pressure air is investigated by two-dimensional particle-in-cell/Monte Carlo collision simulation. It is found that the beam amplitude of RAEs is dictated by the field enhancement factor and the initial energy of electrons obtained near the micro-protrusion is decisive for their converting to RAEs, which precede the low energy electrons and guide the discharge propagation by improving pre-ionization. As a result, the discharge transfers from the filamentary mode without RAEs to the diffuse mode under the high pre-ionization degree due to RAEs and a wide streamer with a diameter comparable with the gap distance is formed, which transfers from spherical to conical shape. The results of this study illustrate the fundamental process of RAE formation and how RAEs influence streamer dynamics during ultra-fast gas breakdown process.

A homogeneous atmospheric pressure air plasma in a 10 mm gap based on a three-electrode configuration

Generation of atmospheric pressure homogeneous air plasma in a large gap (> 4 mm) is a challenge. In this study, an atmospheric pressure homogeneous air plasma generated in a gap up to 10 mm is reported, which is based on a three-electrode configuration, where a high-voltage (HV) electrode and a middle electrode form a surface dielectric barrier discharge (S-DBD), and together with the ground electrode form the main volume discharge. High-speed photographs confirm that the discharge in the main gap is homogeneous. The gas temperature of the plasma estimated from the N2(C3∏u-B3∏g) (Δv = −2) emission is about 320 K, which is close to room temperature. A detailed analysis shows that the discharge ignited between the HV electrode and the middle electrode is serving as an electron source, and the electrons deposited on the dielectric plate are due to the S-DBD along with the applied voltage generating a driving force, which results in a high concentration of seed electrons in the main gap and induces the homogeneous plasma. Further analysis shows that the electric field in the main gap is only about 18.45 kV·cm−1, which is much lower than the typical breakdown electric field of 30 kV·cm−1 for atmospheric pressure air discharge.

Introduction and verification of FEDM, an open-source FEniCS-based discharge modelling code

This paper introduces the finite element discharge modelling (FEDM) code, which was developed using the open-source computing platform FEniCS (https://fenicsproject.org). Building on FEniCS, the FEDM code utilises the finite element method to solve partial differential equations. It extends FEniCS with features that allow the automated implementation and numerical solution of fully coupled fluid-Poisson models including an arbitrary number of particle balance equations. The code is verified using the method of exact solutions and benchmarking. The physically based examples of a time-of-flight experiment, a positive streamer discharge in atmospheric-pressure air and a low-pressure glow discharge in argon are used as rigorous test cases for the developed modelling code and to illustrate its capabilities. The performance of the code is compared to the commercial software package COMSOL Multiphysics® and a comparable parallel speed-up is obtained. It is shown that the iterative solver implemented by FEDM performs particularly well on high-performance compute clusters.

Collective impacts of LPGOD plasma and plasma activated water treatment in rice (Oryza sativa L.)

Combined effects of plasma seed treatment and plasma activated waters (PAW) application on paddy was explored. Low pressure (100 torr) glow oxygen discharge (LPGOD) plasma was used for seed treatment and germination test revealed that 90s seed treatment duration produced highest seed germination of ~96% which is the highest paddy seed germination rate obtained through plasma technology. Plasma activated water (PAW) was prepared with submerged atmospheric pressure air discharge plasma jet. PAW was sprayed 1-5 times to the paddy plants. Field study was divulged that: (a) seed germination percentage was increased by ~10.76% with respect to control; (b) plants growth parameters were enhanced because of combined consequences of plasma seed treatment along with PAW application; (c) defense mechanisms of plants were improved, (d) concentrations of total soluble protein and sugar were increased in the paddy grains, and (d) yield was enhanced by ~16.77%. SAARC J. Agric., 20(2): 17-30 (2022)

Systematic 1D electric field induced second harmonic measurement on primary-to-secondary transition phase of positive streamer discharge in atmospheric-pressure air

The electric field induced second harmonic generation (E-FISH) technique has been widely utilized for the electric field measurement of atmospheric-pressure nonthermal plasmas. However, the measurement accuracy has not been quantified. Further, the E-FISH signal generation that is necessary to the evaluation of the measurement accuracy has been formulated only for the probe laser beam focused by a spherical lens and not for the cylindrical lens. Here, the E-FISH method utilizing the focusing cylindrical lens was studied for accurate one-dimensional (1D) electric field measurement of the primary-to-secondary transition phase of a single-filament positive streamer discharge generated in atmospheric-pressure air. A combination of numerical analysis and the E-FISH signal measurement was used to establish the radial distribution of the electric field vectors and the accompanying measurement accuracy. The E-FISH methodology captured a distinct evolution in the 1D electric field varying over timescales of ns and length scales of 100 µm. At the instant when the primary streamer arrived at the cathode, the electric field at 3 mm above the cathode surface was found to be as high as 225 Td, while the field at 10 mm above the cathode surface was as low as 5 Td. At the final stage of the primary-to-secondary transition phase completed in 3 ns from the primary streamer arrival at the cathode, the electric field at 3 mm above the cathode was found to be lower than that observed at 10 mm from the cathode; this finding is consistent with predictions made based on a previous model describing the initiation of the secondary streamer discharge and previously published electron density measurement.

Kinetic study of key species and reactions of atmospheric pressure pulsed corona discharge in humid air

In this study, we examined the key particles and chemical reactions that substantially influence plasma characteristics. In summarizing the chemical reaction model for the discharge process of N2–O2–H2O(g) mixed gases, 65 particle types and 673 chemical reactions were investigated. On this basis, a global model of atmospheric pressure humid air discharge plasma was developed, with a focus on the variation of charged particles densities and chemical reaction rates with time under the excitation of a 0–200 Td pulsed electric field. Particles with a density greater than 1% of the electron density were classified as key particles. For such particles, the top ranking generation or consumption reactions (i.e. where the sum of their rates was greater than 95% of the total rate of the generation or consumption reactions) were classified as key chemical reactions. On the basis of the key particles and reactions identified, a simplified global model was derived. A comparison of the global model with the simplified global model in terms of the model parameters, particle densities, reaction rates (with time), and calculation efficiencies demonstrated that both models can adequately identify the key particles and chemical reactions reflecting the chemical process of atmospheric pressure discharge plasma in humid air. Thus, by analyzing the key particles and chemical reaction pathways, the charge and substance transfer mechanism of atmospheric pressure pulse discharge plasma in humid air was revealed, and the mechanism underlying water vapor molecules’ influence on atmospheric pressure air discharge was elucidated.

Simulation of negative corona discharge in atmospheric air: from mode of Trichel pulses to stationary discharge

The paper presents a 2D multi-fluid non-stationary model of a negative corona discharge in atmospheric-pressure air in the needle-to-plane diode. Discharges were simulated in gaps up to 1 cm with an applied voltage in the range of 8-100 kV. The simulation results demonstrate two stages of the discharge evolution: a pulsed-periodic stage called the Trichel pulses mode and a stationary glow discharge mode. The spatio-temporal distributions of the discharge plasma and electric field are shown in detail. Physical mechanism of Trichel pulses formation and transition to the stationary discharge are also revealed. The duration of the Trichel pulse mode gradually decreases with increasing of the applied voltage.

Electric field development in positive and negative streamers on dielectric surface

Multiplication of primary electrons at a dielectrics/gas interface exposed to an external electric field leads to the formation of ultra-fast contracted ionisation waves called surface streamers with high local electric field in their microscopic heads. We study this phenomenon in coplanar barrier discharge in atmospheric pressure air where streamers of both polarities are generated simultaneously. The electric field strength development in the discharge is determined experimentally using time-correlated single photon counting enhanced optical emission spectroscopy with high spatiotemporal resolution. We show that very high values of the electric field of even above 1200 Td (approx. 300 kV cm−1) can be a physical reality for positive streamer directly at the dielectric surface. The peak value for negative streamer lies under 200 kV cm−1. In parallel, a two-dimensional fluid model describes the rapidly changing electric field and the spatiotemporal discharge dynamics in good agreement with the experimental results. We also present the theoretical results of spatiotemporal development of electron density and of charge transfer to the dielectric surface via a collapsing sheath as the discharge structure decays within a very few nanoseconds.

Cathode-sheath model for field emission sustained atmospheric pressure discharges

The cathode-sheath region of a discharge in atmospheric pressure air with a flat copper cathode is numerically investigated by using a simple fluid model that takes into account non-local ionization. The effects of the cathode temperature are considered. Results are obtained in a wide current density range of 1–102 A/cm2, which spans from normal glow discharge, through abnormal glow discharge, up to the early stages of the arcing transition. It is shown that the glow-to-arc transition arises from a field-emission instability at the cathode when the current density is larger than ∼10 A/cm2, i.e., when the cathode field exceeds a critical value of about 45 V/μm for the conditions considered. It is also shown that the cathode temperature significantly influences the cathode-sheath region. The proposed model is validated by comparing the numerical results with available experimental data.

Effect of Plasma Activated Water, Hydrogen Peroxide, and Nitrates on Lettuce Growth and Its Physiological Parameters

Cold plasma generated by atmospheric pressure air discharge is a source of various gaseous reactive oxygen and nitrogen species (RONS). When the plasma is generated in a contact with water, the RONS dissolve into water, change its chemical composition, while producing so-called plasma activated water (PAW). The PAW has the potential to be effectively used in various agricultural applications, as the long lived liquid RONS (H2O2, NO2−, NO3−) may act like signaling molecules in plant metabolism or serve as nutrients. We studied the effect of the PAW on lettuce plants and compared it with the effect of H2O2 and/or NO3− solutions of various concentrations to assess their role in the PAW. The PAW was generated from tap water by DC driven self-pulsing transient spark discharge. Pre-grown lettuce plants were cultivated in pots with soil and irrigated with the PAW or solutions of H2O2 and/or NO3−. After 5 weeks the growth parameters, number and quality of leaves, fresh and dry weight of plants, photosynthetic pigment (chlorophyll a + b) content, photosynthetic rate, and activity of antioxidant enzymes (superoxide dismutase, SOD) were evaluated. Lettuce plants irrigated with the PAW in comparison with chemically equivalent solution of H2O2 and NO3− had similar dry weight; however, the PAW induced higher photosynthetic pigment content, higher photosynthetic rate, and lower activity of SOD. The NO3− mainly contributed to the increase of dry weight, photosynthetic pigment content, photosynthetic rate, and overall better appearance of plants. The H2O2 contributed to an increase of dry weight and induced SOD activity. In general, H2O2 and NO3− in proper concentrations can stimulate plant growth and affect their physiological properties.

Formation of Electrohydrodynamic Flow in Corona Discharge of a Three-Cascade Electrode System with Serial and Alternating Connection

In this work, systems with serial and alternating electrical connection of three electrohydrodynamic cells based on corona discharge in atmospheric pressure air were studied. Numerical simulations of the systems was conducted. The volume force acting in the drift regions of the multi-cascade system was calculated and a good agreement was obtained between experimental and theoretical data.

A Two-Dimensional Air Discharge Modified Model Under Unipolar Square Pulse Voltage at Low Temperature and Sub-Atmospheric Pressure

In this paper, a modified COMSOL Multiphysics model with artificial stability is adopted, and the boundary condition developed in the previous paper are applied to the calculation of the photoionization rate. The main processes involved in air discharge were simulated by 39 plasma chemical reactions composed of 12 kinds of particles. The characteristics of low-temperature sub-atmospheric pressure air discharge under unipolar square wave pulse voltage with 13kV applied amplitude, 25 kHz-50 kHz frequency and a duty cycle of 50%-75% are discussed. The results show that: When the duty cycle increases, the average density of electron, N2+, N4+, O2+, O4+, and N2O2+ show an increasing trend, and the average electron temperature changes little; When the frequency increases, the average electron density, the average density of N4+ and O4+ show a downward trend, the average density of N2+, O2+, N2O2+ change little; The average electron temperature shows an increasing trend, but the duration of high electron temperature becomes shorter. When discussing a single period, it is found that the potential difference between the electrode and the plasma determines the direction of the electric field in the space. For the photoionization reaction, even if its influence on the negative streamer is not important, it still needs to be considered in the simulation. The effect of temperature on discharge is also taken as the research emphasis, it includes the following aspects: Firstly, at low temperature, the collision reaction and attachment reaction rates are increased, while the recombination reaction rate is almost unaffected; Secondly, low temperature results in the decrease of secondary electron emission coefficient, which indirectly increases the electric field gradient and the peak value of electric field; Finally, at low temperature, the mobility of carriers, including electrons, positive and negative ions, is increased, but the streamer velocity is decreased.

Textile wastewater treatment by underwater parallel-multi-tube air discharge plasma jet

Textile wastewaters (WW) as released from textile industries damage aquatic environment and thereby create threat to plants and animals. To overcome the problems associated with wastewaters, the plasma technology can be an alternative approach for the reduction of effluents dissolved in textile WWs. In this present study, the degradation of textile dye model WWs is carried out using underwater parallel-multi-tube atmospheric pressure air discharge plasma jet. The investigation reveals that: pH is decreased, while electrical conductivity (EC) is increased in the deionized (DI) waters and model WWs with increasing plasma treatment duration. The Concentrations of O3, H2O2 and NO3- in model WWs are decreased compared to that of DI water with treatment duration, but NO2- is increased. The decrease in O3, H2O2 and NO3- suggest that they participate in the dissociation processes of textile dyes. UV–vis spectroscopic measurements show that almost 70 % of dyes were degraded within 10 min of treatments but the remaining 30 % was taken a longer time. FTIR spectroscopic measurements reveal that the amines and alkynes are likely to be produced through oxidative processes of azo-bonds and nitrogen containing functional groups with the interactions of O3 and OH radical. A fraction of organic nitrogen can be converted to nitrites through oxidation for which the concentration of nitrite is increasing with treatment duration. The proposed environment friendly plasma technology can alternatively be adapted to the reduction of effluents as dissolve in textile WW.

Synthesis of oxygen-containing iron powders and water purification from iron ions by glow discharge of atmospheric pressure in contact with the solution

The formation of precipitation under the action of a direct current atmospheric pressure discharge in air on an iron sulfate (II) solution, which was the cathode and anode, was studied. As turbidimetric kinetics measurements have shown, the process, which proceeds both in the cathode and in the anode, has two stages. At the first stage (slow), a colloidal solution is formed, which then (the second stage, faster) is destroyed with the formation of a flocculent precipitate. The characteristic process times for both stages were found depending on the discharge current, the increase of which led to an increase in the deposition rate. The deposition rate in the cell with a liquid cathode was higher than in the cell with a liquid anode. For this reason, the amount of precipitate formed in the cell with the liquid cathode was greater than in the cell with the liquid anode at the same treatment time. Particle sizes of colloidal solutions and sediments were determined by scanning electron microscopy and dynamic light scattering . The sizes of both colloidal particles and sediment particles for the liquid anode were significantly smaller than for the liquid cathode. X-ray diffraction analysis showed that the precipitations obtained are amorphous, and their calcination turns them into γ-Fe2O3. Based on the data of elemental analysis and others, the composition of micelles was proposed, which included Fe(OH)3, SO4–, and H2O. An analysis of the mechanisms of the processes showed that the most probable chain of transformations involves the oxidation of Fe2+ by HO2 and H2O2 molecules to Fe3+, which irreversibly reacts with OH– to form Fe(OH)3.

Plasma and Gas-Dynamic Near-Electrode Processes in the Initial Phase of a Microstructured Spark Discharge in Air

The results of studies of the dynamics of near-electrode processes in the initial phase of a spark discharge in atmospheric-pressure air in the point-plane geometry are presented. After breakdown, regions of about 50 μm or more in size with an increased electron concentration of (3–8) × 1019 cm–3 near the surface of the flat cathode have been observed. With allowance for the experimental data on erosion effect of the discharge on the surface of a flat electrode and the associated gas-dynamic effects, a physical model of near-electrode processes has been proposed, based on which the gas-dynamic parameters are estimated.

A multi-stage model for dielectric barrier discharge in atmospheric pressure air

A multi-stage model for dielectric barrier discharge in atmospheric pressure air

The relaxation of electrophysical properties HgCdTe epitaxial films affected by plasma of high frequency nanosecond volume discharge in atmospheric-pressure air

In this work the results of the experimental investigation of the influence of the high-frequency nanosecond volume discharge in atmospheric pressure air on the electrophysical properties of epitaxial HgCdTe films are presented. Analysis of magnetic-field dependences of the Hall coefficient have shown that in the near-surface region of the material a high-conductivity n-type layer is formed as a result of irradiation. It is shown that relaxation of the values of the electrophysical parameters of the epitaxial films is observed after the irradiation. The supposition is made that the obtained experimental results may be explained by the formation of thin dielectric oxide film at the surface of the irradiated material, containing built-in fixed and mobile positive charge.

Modelling of an Atmospheric–Pressure Air Glow Discharge Operating in High–Gas Temperature Regimes: The Role of the Associative Ionization Reactions Involving Excited Atoms

A model of a stationary glow-type discharge in atmospheric-pressure air operated in high-gas-temperature regimes (1000 K < Tg < 6000 K), with a focus on the role of associative ionization reactions involving N(2D,2P)-excited atoms, is developed. Thermal dissociation of vibrationally excited nitrogen molecules, as well as electronic excitation from all the vibrational levels of the nitrogen molecules, is also accounted for. The calculations show that the near-threshold associative ionization reaction, N(2D) + O(3P) → NO+ + e, is the major ionization mechanism in air at 2500 K < Tg < 4500 K while the ionization of NO molecules by electron impact is the dominant mechanism at lower gas temperatures and the high-threshold associative ionization reaction involving ground-state atoms dominates at higher temperatures. The exoergic associative ionization reaction, N(2P) + O(3P) → NO+ + e, also speeds up the ionization at the highest temperature values. The vibrational excitation of the gas significantly accelerates the production of N2(A3∑u+) molecules, which in turn increases the densities of excited N(2D,2P) atoms. Because the electron energy required for the excitation of the N2(A3∑u+) state from N2(X1∑g+, v) molecules (e.g., 6.2 eV for v = 0) is considerably lower than the ionization energy (9.27 eV) of the NO molecules, the reduced electric field begins to noticeably fall at Tg > 2500 K. The calculated plasma parameters agree with the available experimental data.