Nanosecond Spark Discharges Research Articles

Fast breakdown process and characteristics diagnosis of nanosecond pin–pin discharge

In this paper, the characteristics of a nanosecond spark discharge with a pin–pin electrode configuration have been systematically studied. Both a streak camera with high temporal resolution and an intensified charge-coupled device (ICCD) camera are employed together to investigate the breakdown and evolution process of the discharge. The formation of initial breakdown and mode transition from streamer to spark in the electrode gap are clearly observed on the time scale of several nanoseconds with a temporal resolution of 100 ps. In addition, the time-resolved spectra technology is also used to analyze the generation and quenching mechanisms of reactive species, the electron density, and the electron temperature. The results show that there is a 1.25 ns initial discharge breakdown and that a bright cathode spot exists before the transformation from streamer to spark channel. After a faster cathode filament and a slower anode filament propagate and merge at the electrode gap, the spark discharge phase begins. The generation processes of different reactive species depend on the discharge phase to a great extent. The N2* is first generated during the streamer phase while the O*, N*, and N+ are mainly generated under the spark phase, in which the electron temperature calculated by Boltzmann plots is 2.74 eV, and the electron density determined from the Stark broadening of O lines is on the order of 1016 cm−3.

Ignition of Carbon Black during Nanosecond Diffuse and Spark Discharges in Air at Atmospheric Pressure

Many scientific teams are currently studying the effects of plasma generated by nanosecond diffuse discharges on the surfaces of various materials in order to modify their properties. To achieve this, uniform plasma is required to act on the target being treated, which is often an electrode in a discharge system. Previously, the surface treatment uniformity of flat electrodes during a nanosecond discharge in a point-to-plane gap was studied by applying a carbon black layer, and a discharge mode was identified in which there was no erosion on the treated electrode. In this study, it was established that during a nanosecond discharge in air at atmospheric pressure in a non-uniform electric field, carbon black deposited on the surface of a flat anode can ignite. The conditions and dynamics of carbon black ignition during the nanosecond discharge were determined. It was observed that the carbon black is ignited on the surface and continues to combust in the gap in the form of flame plumes for tens of milliseconds. It was also found that the combustion of carbon black can occur in both diffuse and spark discharges.

Observation of a Plasma Analogue of the Mpemba Effect

The processes of freezing of water droplets sitting on a substrate after exposure to nanosecond spark discharges have been experimentally studied. It has been found that the droplets subjected to spark discharge treatment freeze much earlier than those unexposed to discharges. The analogy of the observed processes with the well-known Mpemba effect is noted. A qualitative explanation is given for the observed effect: rapid freezing is due to hydrated electrons, which are formed upon contact of water with plasma and play the roleof crystallization centers

Visualization of Liquids Flows in Microfluidics and Plasma Channels in Nanosecond Spark Microdischarges by Means of Digital Microscopy

An application of digital optical microscopes for visualization of single-pulse or pulsed-periodic processes in microfluidics and physics of spark microdischarges is studied. Multiple examples of coagulation processes of liquid microvolumes, nanosecond spark discharges near liquid drops and plant living tissues in a cell-size level are provided.

Triggering of Venus Flytrap With Nanosecond Spark Discharges

This article proposes a contactless method for triggering carnivorous plant Venus Flytrap traps with nanosecond spark discharges generated inside the trap leaflets. It is shown that the sequence of ~1 s of the spark discharges (5.5 kV, 400 A, 100 ns) causes reversible closing of the trap. It is shown that the most important factor of spark discharges is shock waves. This method could be used for the investigation of biomechanics and physiology of insectivorous plants.

The Influence of a Nanosecond Spark Discharge on the Oblique Collision of a Steel Sphere with a Metal Plate

The Influence of a Nanosecond Spark Discharge on the Oblique Collision of a Steel Sphere with a Metal Plate

Влияние наносекундного искрового разряда на косое соударение стального шара с металлической плитой

The effect of a nanosecond spark discharge on the oblique collision of a steel ball and a flat cast-iron plate was experimentally studied. It was discovered that the rebound angle of the ball becomes less than the impact angle at collision with the spark discharge, while the rebound angle is more than the impact angle at the ordinary collision without a discharge.

Optical emission spectroscopy measurement of plasma parameters in a nanosecond pulsed spark discharge for CO2/CH4 dry reforming

In this paper, a nanosecond pulsed spark discharge in CO2/CH4 mixture gas at atmospheric pressure is studied with optical emission spectroscopy. A high-voltage pulse is applied across two plate-shaped electrodes at a repetition frequency of 1 kHz. Emphatically, plasma parameters of this discharge are estimated by spectroscopic methods for giving an insight into the underlying dry reforming reaction mechanism. The time-averaged optical emission is mainly caused by atomic spectral lines of excited O, H, and C+, and C2 swan bands. The vibrational temperature of 8500 ± 50 K and rotational temperature of 3200 ± 100 K are estimated by the excited C2 molecules, respectively. The electron density is calculated by Stark broadening of O (844.6 nm), Hα (656.3 nm), and Hβ (486.1 nm) for 3.4 ∼ 7.71 × 1017 cm−3 while C+ (723.6 nm) for 4.37 × 1018 cm−3 with an electron excitation temperature of 0.58 eV that is estimated by the intensity ratio of Hα and Hβ. The determination of plasma parameters offers essential data for subsequent reaction kinetics research of the plasma-assisted dry reforming of CH4.

An inversion of contact angle hysteresis when a liquid drop slides up on an inclined plane under the spark discharge action

A new physical effect, consisting in the crossover of values and inversion of the dynamic contact angles' hysteresis branches, when a glycerin drop and a water drop slide up a smooth inclined steel plane under the action of nanosecond spark discharges' periodic sequence, was experimentally recorded.

Anchoring of premixed jet flames in vitiated crossflow with pulsed nanosecond spark discharge

This paper deals with the effect of non-equilibrium plasma on the anchoring of a premixed jet flame in hot vitiated crossflow at atmospheric pressure. The turbulent vitiated crossflow was generated by an array of 4×4 premixed turbulent jet flames burning a lean mixture of air and natural gas at an equivalence ratio of 0.7 and a thermal power of 50 kW. The rich jet, with equivalence ratio ϕjet varied between 1 and 3, was injected perpendicularly to the vitiated crossflow in a rectangular duct, with jet-to-crossflow momentum flux ratios J ranging from 1 to 26. A nanosecond repetitively pulsed discharge was initiated in the vicinity of the windward side of the jet root. The effect of discharge power and repetition rate on the lift-off height of the flame is systematically analyzed for different combinations of ϕjet and J. High speed chemiluminescence imaging of the flame and of the discharge shows that the initiation of the discharge on the windward side of the jet enhances the combustion chemistry, reducing the ignition time and the lift-off height of the flame. It is shown that the nanosecond repetitively pulsed discharges are able to maintain a robust anchoring of the flame for a wide range of operating conditions at relatively low electric power cost. Emission spectroscopy and OH-PLIF measurements were carried out to show that the plasma has both thermal and kinetic effects on flame anchoring respectively via intense localized heating of the mixture at temperatures exceeding 3000 K and via an intense production of OH radicals.

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.

Features of the cathode plasma formation at the initial stage of a nanosecond spark discharge in air

Nanosecond discharges at atmospheric pressure have a wide range of applications. The features of a nanosecond spark discharge formation strongly depend on the discharge gap geometry and the applied voltage. The present paper contains the results of near-electrode processes investigation at the initial stage of a spark discharge in air in the pin-to-plate geometry. Extra-high electron concentration in the range of was obtained based on the Mach-Zehnder interferometer after breakdown near the surface of a flat cathode. It is confirmed that the discharge channel is a multitude of microchannels that close the discharge gap. Analysis of a flat electrode surface after breakdown shows that the channel binding region is a cluster of microcraters with diameter from 5 to . A model for the gas dynamics processes at the initial stage of a nanosecond spark discharge is proposed.

Extremely fast formation of anode spots in an atmospheric discharge points to a fundamental ultrafast breakdown mechanism

By employing multi-frame laser interferometry, shadow, and schlieren imaging, we trace the formation of a nanosecond spark discharge in millimeter-sized air gaps formed by a point cathode and flat anode or vice-versa. We discover that the electrical breakdown of the discharge gap is associated with extremely fast (≪1 ns) explosive formation of micron-sized cathode and anode spots. We find that the characteristic delay between the instants of the anode and cathode spot initiation can be much shorter than 1 ns. The spots appear as highly ionized near-electrode plasmas with an electron density ne ∼ 1019–1020 cm−3. The spots then give rise to highly ionized spark channels with pronounced filamentary structures. Our findings indicate that the extremely fast formation of anode spots is associated with an ultrafast gap breakdown promoted by an ultrafast ionization wave (UFIW). The role of the UFIW governed by the rapidly evolving cathode spot is discussed as a fundamental mechanism of the breakdown.

Effect of gas pressure and pulse duration on dry reforming of methane in nanosecond spark discharge

This paper presents the results of experiments on dry reforming of methane under the action of a nanosecond spark discharge at medium pressures up to 5 atm. High-voltage pulse generators with pulse length of 1 to 15 ns and voltage pulse amplitude of 50 to 200 kV were used to power the discharge. It was demonstrated that the spark discharge efficiency significantly exceeds the corona and diffuse discharge efficiency. With increasing pressure, the methane conversion value decreases, and the specific energy consumption increases. As the pulse length increases, the conversion value increases due to the increase in the energy deposition in the gas. The lowest energy consumption for the conversion of a methane molecule was 20 eV per molecule at pressure of 1 atm and discharge pulse length of 15 ns.

Spatial evolution of the plasma kernel produced by nanosecond discharges in air

This work presents an experimental investigation of the hydrodynamic effects induced by nanosecond and conventional spark discharges. The energy deposited in sparks in the short breakdown time (~1 mJ mm−1) induces hydrodynamic effects that redistribute the energy over a large volume (~1 cm3) surrounding the initial plasma channel. This process influences the subsequent formation of the ignition kernel and the initiation of combustion. The experimental results presented in this paper were obtained with a set of synchronized diagnostics including schlieren, OH planar laser induced fluorescence and electrical measurements of the energy deposited in the plasma. It is shown that the motion of the gas excited after the discharge breakdown depends not only on the total deposited energy but also on the dynamics of the energy input in the plasma. Finally, the effects of nanosecond sparks are compared with those of conventional sparks used for internal combustion engines. We show that, with 20 times less energy, the nanosecond spark produces a twice bigger excited gas volume than the conventional spark. This is because the energy deposited by the nanosecond spark during the breakdown stage is three times higher than for the conventional spark.

Generating Periodic Pulse Sequences of Nanosecond Spark Discharges in an Air Gap between Transparent Hydrogel Electrodes

Hydrogel electrodes transparent in the visible range have been used for the first time to generate periodic sequences of nanosecond pulsed spark discharges with current amplitude up to 400 A at a 250-Hz repetition frequency. Video images of the discharge and craters formed on the surface of hydrogel electrodes are presented.

Coalescence of Liquid Droplets Under Effect of Pulsed-Periodic Spark Discharges

Nanosecond spark discharges between the liquid droplets of different colors located on a dielectric substrate are studied. The investigation is carried out by means of the video visualization method. It is shown that during several seconds of the discharge motion with a frequency of 250 Hz, the droplets’ coalescence occurs via the stage of a water bridge creation. In case of having two droplets with identical liquid, the mixing of their contents takes place. There is no mixing in case of different liquids such as glycerin and water or glycerin and red beet juice.

Crystallization Features of Aqueous Solutions in Their Droplets Evaporated by Nanosecond Spark Discharge Treatment

Crystallization processes that occur during the drying of droplets of solutions by treating with nanosecond spark discharges have been experimentally investigated. It has been shown that crystallization in the droplets under plasma treatment proceeds in a different way than in identical droplets dried in the conventional mode.

Plasma as a Surfactant: A New Capillary Effect and a New Wetting Effect Induced by Nanosecond Spark Discharges

The influence of nanosecond spark discharges on liquids and we found that their produced plasma can behave as a nonchemical surfactant was studied. Essentially, we discovered two plasma-induced effects: a new capillary effect that leads to a liquid rising unexpectedly high in a capillary and a new wetting effect that induces a peristaltic motion of a liquid droplet on a solid surface. These effects can give rise to new applications in the liquid medicine technology and be useful for solving the water pollution problem.

Producing of Microbubbles in Dried Juice Droplets Treated With Nanosecond Spark Discharges

We studied the influence of plasma nanosecond spark discharges on dried juice droplets. Our samples were juices made of grape, tangerine, lemon, aloe, and beetroot, and also coffee. It is found that all dried droplets treated with discharges form microbubbles. We studied the dynamics of microbubble development and estimated their growth rate in order to determine their shape and internal structure. It was established that bubbles have an almost spherical shape and that they are hollow and thin walled. The walls of microbubbles are elastic, while they are filled with a gas. We think that our microbubbles have a hole at the bottom. The microbubble walls are essentially made of dried juices, which can be obtained from edible fruits. A potential application for such microbubbles can be capsules for small doses of drugs.