Negative Pulsed Discharge Research Articles

The propagation of negative pulsed discharges facilitated by artificially injected gas bubble in water

Abstract The artificial injection of bubbles into the electrode gap can effectively enhance the performance of underwater pulsed spark discharge (UPSD). It is crucial to investigate the morphology and propagation characteristics of discharges for a comprehensive understanding of bubble-stimulated UPSD. This paper presented an extensive study of negative discharges facilitated by the injected large bubble (with a diameter of 3 mm) in UPSD. The bridging effect of the bubble and the morphology and propagation of discharges were observed through the shadowgraph images captured by a high-speed camera. A numerical model was built to analyse the influence of the bubble on the initial electric field distribution between the electrodes. The characteristics of discharges were notably influenced by bubble parameters and energization conditions. Not in all cases could the bubble play the bridging effect role. The effective range of the bubble was roughly confined to a small region near the HV electrode tip. The experimental results obtained in this paper have certain guiding significance for the practical application of UPSD.

Impact of surface charges on energy deposition in surface dielectric barrier discharge: a modeling investigation

Surface charges have significant impact on the evolution of surface dielectric barrier discharge (SDBD). In this work, the role of residual surface charges on repetitively nanosecond pulsed SDBD in atmospheric air is investigated using a two-dimensional fluid model, based on the assumption of preserving the distribution of surface charges at the end of the previous high voltage (HV) pulse. In the bipolar mode when the polarity of residual surface charges is opposite to that of the current HV pulse, a lower breakdown voltage and more deposited energy can be observed, showing an obvious enhancement of SDBD. In the unipolar mode, residual surface charges suppress the development of discharges and energy deposition. It is found that more residual surface charges are accumulated during the negative pulsed discharge, which have a more pronounced effect on the subsequent positive pulsed one. This is explained by the fact that the negative surface streamers directly contact the dielectric and charge it, while the positive surface streamers float above the dielectric, forming a ion-rich region near the surface. The results in this work demonstrate the mechanism of how residual surface charges affect discharge dynamics, which can be utilized to regulate energy deposition in SDBDs.

Electron density and electron temperature measurements in an atmospheric pressure plasma interacting with liquid anode

Plasma driven solution electrochemistry has received increasing attention during the last decade for a variety of applications including nanomaterial synthesis. We report the temporal and spatial resolved electron density and temperature for a negative pulsed DC discharge in helium with N2 shielding gas impinging on a liquid anode as measured by Thomson scattering spectroscopy. A stable radial plasma contraction and significant plasma-enhanced N2 mixing was found for the longest investigated pulse width (9 μs). It was found that the plasma enhanced N2 mixing significantly impacts the plasma morphology and electron properties. In addition, we observed a significant increase in electron temperature coinciding with a drop in electron density near the liquid anode surface, which is attributed to electron attachment and electron-water ion cluster recombination enhanced by plasma-induced water evaporation. This near anode surface phenomenon is argued to be responsible for the discharge stabilization by preventing the development of a thermal instability in spite of the significant gas heating. This increase in electron temperature near the anode suggests the presence of a significant flux of hot electrons into solution which might enable non-equilibrium electron-driven reactions in the liquid phase.

Carbon nanotube deposition through intermittent high voltage pulsed electrophoresis on jute fibre

Electrophoretic deposition is an efficient, high-level process for the manufacture of films or coatings from colloidal suspensions. In this process, electrophoretically deposited materials exhibit good microstructure homogeneity and high packing density. The effect of Carbon Nanotubes (CNT) deposition through intermittent high voltage Electrophoretic Deposition (EDP) on the Jute Fibre (JF) surface is analysed. This is a method adapted from the conventional EDP process. Therefore, two parameters, such as pulse type and medium type, are evaluated to obtain an effective and uniform CNT deposition on the JF surface. The pulse types are positive pulse discharge and positive and negative pulse discharge. Both pulses are intermittent and delivered at high voltages. On the other hand, two medium types were considered. The first is composed of CNT and deionized water, and the other is composed of CNT, Sodium Dodecyl Sulfate (SDS), and deionized water. According to the microscopy results and TG, it is clear that the introduction of SDS on the medium, under positive and negative pulse discharge, provided an effective and homogeneous CNT deposition onto the JF surface. As a result of good CNT deposition, it was an enhancement in electrical conductivity and an increase in oxygen functional groups compared to untreated JF. Also, the JF became hydrophobic.

Effects of humidity on the dynamics and electron recombination of a pin-to-pin discharge in He + H2O at atmospheric pressure

Control of the plasma chemistry is essential for the effectiveness of atmospheric pressure plasmas in many applications. For this, the effects of the humidity of the feed gas on the discharge chemistry need to be considered. Detailed studies are scarce and many of them are dominated by surface interactions, obscuring any volume effects. Here, a negative nanosecond pulsed discharge is generated in a pin–pin 3 mm gap geometry in He + H2O that enables the study of volume kinetics due to minimal surface area. The effect of humidity on the discharge development, electric field and electron density is investigated through experiments and modelling. It is found that the presence of water vapour affects both the electron density at the start of the pulse (remaining from the previous pulse) and the ionisation rates during the ignition phase, leading to a complex dependence of the discharge development speed depending on the water concentration. The electron decay is studied using the 0D global kinetics model GlobalKin. The dominant reactions responsible for the electron decay depending on the concentration of water vapour are determined by comparing experimental and simulated results and these reactions are grouped in simplified kinetic models. It is found that with water concentrations increasing from 0 to 2500 ppm, the complexity of the dominant reactions increases with in particular O2 +, H2O3 + and water clusters becoming important for high water concentrations. This work also provides experimental data for validation of kinetic models of plasmas in controlled environments.

Time-resolved analysis of negative pulsed discharges in water: streamer initiation and propagation modes

Analyses of the initiation and propagation-mode transitions of negative streamers are essential to develop a thorough understanding of underwater pulsed discharges. This paper presents experimental observations of negative streamers in deionized water performed using time-resolved visualization and electrical measurements. Based on the distributions of discharge inception delay and quantitative calculations of the ionization initiation fields, a streamer initiation model combining Zener ionization and field emission processes is proposed to account for discharges with short inception delays (<200 ns). Joule heating is the main mechanism responsible for discharges with an inception delay on the order of microseconds. The evolutions of bushy streamer morphology show that streamers exhibit more uniform structures under higher voltages, as most of the streamer branches grow simultaneously. A large-area discharge of bushy streamers is observed and is speculated to be closely related to the charge dynamics at the gas/liquid interface. The propagation of filamentary streamers and the transitions from filamentary to bushy streamers are presented. The redistribution of deposited charge and mitigation of the electric field during branching are the main causes for the mode transitions of streamers.

INVESTIGATION OF OZONE SYNTHESIS IN THE NEGATIVE PULSED CORONA DISCHARGE IN OXYGEN AT THE COMBINED SUPPLY VOLTAGE

The influence of combined supply voltage parameters (bias voltage and voltage pulse amplitude) on efficiency of ozone synthesis in the negative pulsed corona discharge in oxygen was obtained. Pulse overvoltage led to intensification of discharge processes. Bias voltage applied during the discharge channel relaxation essentially increased the efficiency of ozone synthesis. It was established that the “optimal” bias voltage which provides maximum ozone generation doesn’t depend on voltage pulse amplitude, but depends on input oxygen concentration and generated ozone concentration.

Electrical characterization of positive and negative pulsed nanosecond discharges in water coupled with time-resolved light detection

Electrical discharge in liquids is a research field that has great potential in environmental and technological applications. Depending on the experimental conditions (liquid nature, interelectrodes distance, applied voltage, pulse width, etc.), various discharge modes can be obtained. The involved physical processes have relatively fast spatiotemporal dynamics and, therefore, are not well understood. In this study, we report the electrical characterization, coupled with time-resolved light detection (using a photomultiplier, PM, tube), of positive and negative pulsed nanosecond spark discharges in de-ionized water using copper electrodes (distanced by ∼50 μm) in a pin-to-plate configuration. A detailed analysis of the current–voltage waveforms during the pre-breakdown and the breakdown phases is shown, and we found that the pre-breakdown phase depends on the high voltage magnitude only for positive polarity. On the other hand, the PM signals showed dependence on the voltage magnitude and on the pulse width, and various emission phases are observed. These phases can be related to the discharge power and/or to the discharge current. Filtered PM signals at various wavelengths are also acquired, and their temporal dynamics are discussed regarding the discharge conditions.

Measurements of electric field in an atmospheric pressure helium plasma jet by the E-FISH method

Temporal and spatial distributions of the electric field in an atmospheric pressure, ns pulse, positive and negative polarity helium plasma jets are measured by ps electric field induced second harmonic generation. The measurements have been done in a quasi-two-dimensional plasma jet impinging on liquid water, using a laser sheet and a focused laser beam positioned at different heights above the water surface. Absolute calibration of the electric field is obtained by measuring a known Laplacian electric field distribution for the same geometry and at the same flow conditions. The vertical component of the electric field is determined by isolating the second harmonic signal with the vertical polarization. The measured electric field is averaged over the span of the plasma jet, in the direction of the laser sheet or the focused laser beam. The spatial resolution of the laser sheet measurements is approximately 15 μm across the sheet, with the temporal resolution of 10 ns. The spatial resolution of the focused laser beam measurements is approximately 180 μm across the beam, with the temporal resolution of 2.5 ns. The results show non-monotonous electric field distribution across the jet, with two maxima produced by the surface ionization waves propagating over water. Considerable electric field enhancement is detected near the surface. Residual charge accumulation on the water surface is detected only in the negative polarity pulse discharge. The results provide new insight into the charge species kinetics and transport in atmospheric pressure plasma jets, and produce data for detailed validation of high-fidelity kinetic models.

Comparative study of positive and negative pulsed discharge plasma characteristics of coaxial gun

The coaxial gun plasma generated by pulsed discharge possesses the characteristics of high speed and high density, and has potential application value in the field of fusion, space propulsion and astrophysics. In this paper, the effect of positive and negative pulsed discharges on plasma characteristics are investigated and a theoretical model for analyzing the morphology of positive and negative pulsed current sheets is proposed. Positive and negative pulsed discharges are realized by changing the direction of the rectifier diode in the pulse power supply to change the direction of the recharging current. Through theoretical analysis, and measurements by using photodiode, Pearson probe, magnetic probe, HD camera, fast-framing camera and RGB image processing, the plasmas generated by positive and negative pulsed discharges are compared and investigated. Most of experimental diagnoses concentrate on investigating the plasma behavior in the coaxial gun muzzle on a microsecond-order time scale. Because radial and axial transport characteristics of plasma change little, we think, the plasma characteristics in the muzzle still depend on the characteristics of plasma in the coaxial gun. Therefore, the conclusion of the theoretical analysis of the current sheet in the coaxial gun is still valid for the plasma in the muzzle. The theoretical analysis shows that the positive pulsed current sheet presents a parabolic shape and the negative pulsed current sheet displays a convex shape, which makes the negative pulsed current sheet sweep more efficiently and a large amount of plasma is concentrated near the inner electrode, namely the cathode, so the negative pulsed plasma is denser. For the positive pulsed plasma, near the inner electrode the plasma is thin and the magnetic pressure is powerful, and near the outer electrode, the plasma is dense and the magnetic pressure is weak. Therefore, the positive pulsed plasma is faster in movement speed but easier to split, and because of its dispersion, its transport stability is not so good as that of the negative pulsed plasma. The experimental results accord with the theoretical analyses. The final conclusion shows that under the same discharge parameters, the positive pulsed discharge produced plasma is faster in movement speed but more likely to split, and the negative pulsed discharge created plasma is denser in density and more stable. Therefore, for obtaining a higher density plasma, the negative pulsed discharge is recommended, and for achieving a high-speed plasma source, the positive pulsed discharge is advised to be adopted.

Mechanism of pH Variation and H2O2 Generation in Water Exposed to Pulsed Discharge Plasma

Positive and negative pulsed discharge plasma is generated above test liquid containing NaCl in Ar atmosphere, and the spatiotemporal variation of pH value in the liquid is visualized by a colorimetric method using bromothymol blue. Furthermore, polarity effects on H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> generation are examined by electrochemical calculation and a colorimetric method using titanium sulfate. When the positive pulsed discharge plasma is generated, the pH value of the liquid is decreased by H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> generation through the dissociation of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , formed by the charge exchange reaction between Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O, while the pH value of the vicinity of an earthed electrode is increased by OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> generation through the electrolysis of water. When the negative pulsed discharge plasma is generated, the pH value of the liquid is increased by OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> generation and H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> reduction, respectively, through the reaction of hydrated electrons with H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , while the pH value in the vicinity of the earthed electrode is decreased by H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> generation through the electrolysis of water. The generation of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is found to be promoted when the positive pulsed discharge plasma is generated, and this increase rate of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is in approximate agreement with the calculated generation rate of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , which is produced from OH generated by electrolysis.

Spectroscopic diagnosis of plasma in atmospheric pressure negative pulsed gas-liquid discharge with nozzle-cylinder electrode

The plasma characteristics of a gas-liquid phase discharge reactor were investigated by optical and electrical methods. The nozzle-cylinder electrode in the discharge reactor was supplied with a negative nanosecond pulsed generator. The optical emission spectrum diagnosis revealed that OH (A2∑+ → X2Π, 306–309 nm), N2 (C3Π→B3Πg, 337 nm), O (3p5p→3s5s0, 777.2 nm) and O (3p3p→3s3s0, 844.6 nm) were produced in the discharge plasma channels. The electron temperature (Te) was calculated from the emission relative intensity ratio between the atomic O 777.2 nm and 844.6 nm, and it increased with the applied voltage and the pulsed frequency and fell within the range of 0.5–0.8 eV. The gas temperature (Tg) that was measured by Lifbase was in a range from 400 K to 600 K.

Plasma Actuator Performance Driven by Dual-Power Supply Voltage—AC High Voltage Superimposed With Pulse Bias Voltage

Many studies have demonstrated the utility of surface dielectric barrier discharge (SDBD) plasma actuators driven by different voltage waveforms for airflow control. In this paper, a new dual-power supply voltage consisting of ac high voltage with a superimposed positive or negative pulse bias voltage is applied to a two-electrode structure SDBD actuator to compare the actuator performance with that driven by a single ac voltage waveform. The ionic wind velocity, the thrust force, and the schlieren visualization images are studied under three types of voltage waveforms: single ac voltage, ac voltage superimposed with a positive pulse bias voltage (ACPP), and ac voltage superimposed with a negative pulse bias voltage (ACNP). The influences of different pulse parameters including pulse voltage, pulse repetition frequency (PRF), and pulsewidth on the actuator performance are studied in detail. Experimental results show that pulse voltage and PRF have more notable influence on the actuator performance when the actuator is driven by ACPP, while the pulsewidth has little effect on the actuator performance. In contrast, the actuator performance is little changed when the actuator is driven by ACNP. The positive and negative pulse discharges have different effects on the actuator performance, the reason is positive pulse discharge increases the discharge of glow-like region while negative pulse discharge increases the discharge of streamer region in the following ac cycle. The schlieren images further indicate pulse discharge exerts its effects on the SDBD actuator performance by affecting the electric field of ac discharge.

The discharge characteristics of surface dielectric barrier discharge sustained by repetitive nanosecond pulses in open air

A nanosecond pulsed surface dielectric barrier discharge (NPSDBD) is a promising method for flow control and combustion. We systematically investigated the influence of pulse parameters on the discharge characteristics of NPSDBD, especially on the conduction current of discharge and the energy deposition curves. Meanwhile, the differences of the characteristics of the discharge generated by positive pulses and negative pulses are focused in this paper. The underlying physics is also discussed. Four different discharge regimes of NPSDBD are presented, which can be distinguished by the temporal emission behaviors of discharge and the conduction current of discharge. The transitions of four discharge regimes were also investigated by changing the pulse amplitude, repetitive rate, and voltage polarity. It was found that it is easier to translate quasi-uniform discharge to filamentary discharge or transition mode for the repetitive pulses with a negative polarity. A phenomenological model was proposed to explain the differences between a positive repetitive pulse discharge and a negative repetitive pulse discharge.

Corona discharge initiation for TV control of defects in crystalline silicon

The article presents the results of experimental studies to control of defects of monocrystalline silicon wafers. Monocrystalline silicon is one of the major solar energy materials. Therefore, control of its defects is an important task that leads to saving of production resources and reduce the cost of photovoltaic solar cells put into operation. Defects in the wafer of monocrystalline silicon are observed under the excitation of negative pulsed corona discharge in the air gap over them. This method of corona discharge excitation in the planar electrode system with a dielectric insulating wafer allows adjusting the voltage and current of the discharge. A feature of the proposed method is to produce a corona discharge at a relatively low voltage of 1-1,5 kV. Using a transparent electrode makes it possible to observe defects and measure their brightness and geometrical parameters of the corona via TV information and measuring system. In particular, the authors have observed the luminescence of the defects in the crystalline silicon wafer under the excitation of negative pulsed corona discharge in the air. The results can be used to control the silicon wafers in the manufacture of photovoltaic solar cells.

Fluorescence detection of hydroxyl radicals in water produced by atmospheric pulsed discharges

It has been proven that hydroxyl (OH) radicals can be generated by streamer discharges across water surfaces under ambient atmospheric conditions. Hydroxyl radicals have the highest oxidation capability amongst all oxygen-based reactive species, thus OH play an important role in oxidation of organic molecules and the bactericidal effects of plasma discharges. In this study, generation of hydroxyl radicals in water by pulsed streamer discharges was investigated. Terephthalic acid was used as a chemical probe as this acid is converted into 2-hydroxyterephthalic acid (HTA) by chemical reaction with OH radicals. The concentration of OH radicals was quantified by measuring the fluorescence light intensity generated by HTA molecules in water solutions. Both positive and negative pulsed discharges with different voltage levels were tested. Two different types of sample holder – non-conductive plastic dishes, and dishes lined with conductive aluminum foil – were used in order to investigate the effect of the discharge propagation path on the efficiency of OH production. The efficiency of OH production was measured as a function of: the distance between the needle electrode and the water surface; the magnitude and polarity of HV energization; and the total delivered charge. The obtained results will help in optimization of non-thermal plasma systems for chemical and biological decontamination.

Effect of Pulse Polarity on Nanosecond Surface Dielectric Barrier Discharge

This paper presents the optical emission characteristics of a surface dielectric barrier discharge sustained by repetitive nanosecond pulses with different polarities in the subsonic airflows. The plasma images presented here show that the positive polarity pulsed discharge is stable in the airflows, appearing as a brush-type discharge. While the negative polarity pulsed discharge plasma becomes a filamentary pattern that is evidently spatial inhomogeneous in quiescent air, it behaves unstable in airflows.

Resistance Models Applied to the Return Stroke Phase of Negative Pulsed Surface Discharges in Air

The energy deposition during the return stroke phase of a pulsed surface discharge is driven by the electrical circuit and the electrical properties of the discharge. To control these factors, a parametric study is performed with varying the circuit parameters, for different discharge lengths and voltages between -19 to -26 kV. The electrical characteristics of the discharge are then simulated using different plasma resistance models, which assume a time-varying resistance: the Toepler model, the Rompe-Weizel model, and the Vlastós model. The model parameters are optimized to fit the experimental results. The analysis shows that for long pulses obtained with large inductance, the three models fare equally well, since the discharge resistance is mainly constant during the pulse. In low-inductance cases, the Toepler model leads to larger errors during the initial current pulse, whereas the Rompe-Weizel and Vlastós models describe with a good agreement the experiments. The discharge resistance evolves during the first 300 ns, then remains mostly constant until the end of the pulse. The constant part of the resistance gives the surface-averaged conductivity of the discharge, which increases linearly with the linear energy dissipated in the discharge. Finally, theoretical estimates of the varying resistance parameters are in fair agreement with the parameters obtained while fitting the experiments, in particular in the Rompe-Weizel case. These findings can be used to estimate the channel resistance of a pulsed surface discharge, and to help optimizing the high-voltage circuit.

Prebreakdown process of a negative nanosecond pulsed discharge in supercritical carbon dioxide

The prebreakdown process in a 100 µm gap in supercritical carbon dioxide was investigated under negative nanosecond pulsed voltage. A bushlike negative streamer was observed by the shadowgraph method. Although currents flowed in the middle of the rising edge, a back discharge current suddenly appeared at the falling edge when a peak voltage exceeding 28 kV was applied. Electron multiplication was estimated to be approximately 108 by integrated calculation of the back discharge current. These results suggest that a negative streamer grows by steps and the inside of the bush streamer is considered to consist of a high-pressure gas.

Diagnosis of hydroxyl radicals and the treatment of Acid Orange Π in negative pulsed discharge

A kind of device supplied with negative pulsed high voltage was designed for water treatment. The nozzle discharge electrode was supplied with high voltage and the cylinder wall of the treatment chamber was grounded. Since the non-thermal plasma, especially, hydroxyl radicals played the dominant role in removing pollutants in the water by discharge plasma, hydroxyl radicals were measured in the negative pulsed discharge process by the optical emission spectroscopy (OES) effects of the repetition rate and the peak value of the pulsed discharge on the hydroxyl radicals' production and the decomposition rate of the Acid Orange Π solution were studied.