Filamentary Dielectric Barrier Discharge Research Articles

The interaction between filaments in dielectric barrier discharge excited by bipolar/unipolar nanosecond pulse powers

This study investigates the behavior of discharge filaments in dielectric barrier discharges with a focus on the effects of nanosecond pulse voltage polarity. We observed significant repulsion between discharge filaments when the pin electrode was grounded in bipolar nanosecond pulse discharge. The tilt angle of the filaments was directly proportional to the peak current, which is indicative of charge density. When the bare pin electrode acted as an H.V. electrode, the repulsion phenomenon was diminished. Surface charges released through the bare pin electrode instead of accumulated on the dielectric surface accounts for this phenomenon. The study also highlights the impact of bipolar versus unipolar nanosecond pulse powers. The addition of a water resistor (WR) results in a slower falling edge of the pulse voltage and the absence of subsequent reverse discharges. The repulsion between filaments disappears both in pin-to-ground discharge and pin-to-H.V. discharge. The introduction of WR leads to a reduction of the current pulse’s duration and a premature termination of the discharge process, resulting the influence of surface charges on filament positioning negligible. It is hypothesized that the spatial distribution of ions does not exhibit significant repulsion, attributed to their substantial mass and sparse distribution in space.

On the chronological understanding of the homogeneous dielectric barrier discharge

AbstractDielectric barrier discharges (DBD) are widely utilised non‐equilibrium atmospheric pressure plasmas with a diverse range of applications, such as material processing, surface treatment, light sources, pollution control, and medicine. Over the course of several decades, extensive research has been dedicated to the generation of homogeneous DBD (H‐DBD), focussing on understanding the transition from H‐DBD to filamentary DBD and exploring strategies to create and sustain H‐DBD. This paper first discusses the influence of various parameters on DBD, including gas flow, dielectric material, surface conductivity, and mesh electrode. Secondly, a chronological literature review is presented, highlighting the development of H‐DBD and the associated understanding of its underlying mechanisms. This encompasses the generation of H‐DBD in helium, nitrogen, and air. Lastly, the paper provides a brief overview of multiple‐current‐pulse (MCP) behaviours in H‐DBD. The objective of this article is to provide a chronological understanding of homogeneous dielectric barrier discharge (DBD). This understanding will aid in the design of new experiments aimed at better comprehending the mechanisms behind H‐DBD generation and ultimately assist in achieving large‐volume H‐DBD in an air environment.

Enhancing the physicochemical properties and reactive species concentration of plasma activated water using an air bubble diffuser

Present study investigates the enhancement in plasma-activated water (PAW) properties (physicochemical properties and reactive oxygen-nitrogen species (RONS)) using bubble diffuser. In one setup, the diffuser attaches to the pencil plasma jet (PPJ) and producing discharge gas bubbles in water. In another setup, the bubbler agitates water during plasma-water interaction. Filamentary dielectric-barrier discharge (DBD) in the PPJ becomes diffusive DBD with bubbler agitation, resulting in higher discharge current and lower voltage. PAW (bubbler) exhibits enhanced physicochemical properties and reactive species (except H2O2). Bubbler-agitated PAW demonstrates substantial increases in properties and reactive species (75.4% NO3−, 702.4% NO2−, 1600% H2O2, 368.3% O3). Bubble diffuser enhances PAW technology for diverse applications.

Formation mechanisms of striations in a filamentary dielectric barrier discharge in atmospheric-pressure argon

Formation mechanisms of striations along the discharge channel of a single-filament dielectric barrier discharge (DBD) in argon at atmospheric pressure are investigated by means of a time-dependent, spatially two-dimensional fluid-Poisson model. The model is applied to a one-sided DBD arrangement with a 1.5 mm gap using a sinusoidal high voltage at the powered metal electrode. The discharge conditions are chosen to mimic experimental conditions for which striations have been observed. It is found that the striations form in both half-periods during the transient glow phase, which follows the streamer breakdown phase. The modelling results show that the distinct striated structures feature local spatial maxima and minima in charged and excited particle densities, which are more pronounced during the positive polarity. Their formation is explained by a repetitive stepwise ionisation of metastable argon atoms and ionisation of excimers, causing a disturbance of the spatial distribution of charge carriers along the discharge channel. The results emphasise the importance of excited states and stepwise ionisation processes on the formation of repetitive ionisation waves, eventually leading to striations along the discharge channel.

Interplay between nitrogen oxides and ozone in a filamentary dielectric barrier discharge at various frequencies

AbstractPursuing more efficient nitrogen fixation in the context of the current climate crisis is of prime importance. The Haber‐Bosch process (NH3 production) accounts for at least 2% of the yearly released greenhouse gases. Alternatively, different atmospheric nonthermal discharges have proven their ability to convert nitrogen and oxygen from the air into nitrogen oxides (NO, NO2, and HNO3 hereafter referred as NOx). Among them, dielectric barrier discharges (DBDs) in N2/O2 are very interesting as they are characterized by microdischarges (MDs) developing into filaments under specific conditions (gap length, voltage, frequency, nature of the dielectrics). In this work, we used a sinusoidal voltage at 4, 12, 17.5, and 30 kHz as a key parameter to manipulate the MDs behaviors in an N2/O2 DBD and tailor the chemistry of the discharge. We characterized the MDs distribution by high‐speed camera imaging. Two different nitrogen emission systems, that is, the second positive system (SPS) and the first negative system (FNS), were used to assess the filament temperature and what we define as the delayed‐glow temperature, respectively. The influence of the filament's distribution on the overall discharge temperature has also been evaluated, by using a novel approach allowing the generation of heat distribution maps directly on a thermosensitive paper exposed to the discharge. Finally, the effect of the filaments on ozone (O3) and NOx production has been monitored by in situ Fourier‐transform infrared (FTIR). The DBD can be tuned between homogenously distributed MDs at 4 and 12 kHz to highly localized filaments at 17.5 and 30 kHz. A high filament temperature combined with a cold delayed‐glow is observed at 17.5 kHz while both the filament and the delayed‐glow temperature are high at 30 kHz. Low frequencies lead to heat spreading into the whole discharge volume, while localization of heat along the filament's paths is observed at high frequencies. High‐temperature filaments in the 30 kHz discharge and in the globally heated discharge at low frequencies quickly remove O3 from the discharge and consequently limit the overall NOx production by removing important oxidation pathways. On the contrary, filaments surrounded by cold gas observed at 17.5 kHz allowed to maintain a high concentration of O3 necessary for a faster oxidation of NO and thus increase the HNO3 production, even after 250 s, by avoiding backward reactions.

Simple and Scalable Chemical Surface Patterning via Direct Deposition from Immobilized Plasma Filaments in a Dielectric Barrier Discharge.

In this work, immobilization of the often unwanted filaments in dielectric barrier discharges (DBD) is achieved and used for one‐step deposition of patterned coatings. By texturing one of the dielectric surfaces, a discharge containing stationary plasma filaments is ignited in a mix of argon and propargyl methacrylate (PMA) in a reactor operating at atmospheric pressure. From PMA, hydrophobic and hydrophilic chemical and topographical contrasts at sub‐millimeter scale are obtained on silicon and glass substrates. Chemical and physical characterizations of the samples are performed by micrometer‐scale X‐ray photoelectron spectroscopy and infrared imaging and by water contact angle and profilometry, respectively. From the latter and additional information from high‐speed imaging of the plasma phase and electrical measurements, it is suggested that filaments, denser in energetic species, lead to higher deposition rate with higher fragmentation of the precursor, while surface discharges igniting outwards the filaments are leading to smoother and slower deposition. This work opens a new route for a one‐step large‐area chemical and morphological patterning of surfaces at sub‐millimeter scales. Moreover, the possibility to separately deposit coatings from filaments and the surrounding plasma phase can be helpful to better understand the processes occurring during plasma polymerization in filamentary DBD.

Automated Fluid Model Generation and Numerical Analysis of Dielectric Barrier Discharges Using Comsol

MCPlas is introduced as a powerful tool for automated fluid model generation with application to the analysis of dielectric barrier discharges operating in different regimes. MCPlas consists of a number of MATLAB\textsuperscript{\textregistered} scripts and uses the COMSOL Multiphysics\textsuperscript{\textregistered} module LiveLink\textsuperscript{\texttrademark} for MATLAB\textsuperscript{\textregistered} to build up equation-based COMSOL Multiphysics\textsuperscript{\textregistered} models from scratch. The present contribution highlights how MCPlas is used to implement time-dependent models for non-thermal plasmas in spatially one-dimensional and axisymmetric two-dimensional geometries and stresses out the benefit of automation of the modelling procedure. The modelling codes generated by MCPlas are used to study diffuse and filamentary dielectric barrier discharges in argon at sub-atmospheric and atmospheric pressure, respectively. The seamless transition between different levels of model complexity with respect to the considered model geometry is demonstrated. The presented investigation of a single-filament dielectric barrier discharge interacting with a dielectric surface shows that complex phenomena of high technological relevance can be tackled by using plasma models implemented in COMSOL Multiphysics\textsuperscript{\textregistered} via MCPlas.

Modifications of an electrolytic aluminum oxide film under the treatment with microdischarges during plasma electrolytic oxidation, a self-organized dielectric barrier discharge (DBD) and a DBD-like plasma jet

A key to the understanding of mechanisms during plasma electrolytic oxidation (PEO) is the interaction between microdischarges and an amorphous oxide film. The PEO microdischarges, which are randomly distributed on the surface of a treated lightweight metal substrate (Al, Ti, Mg), cause material extraction and support the formation of hard and dense crystalline oxide films. Characterization of these microdischarges is a complicated task under PEO conditions, because of the stochastically temporal and spatial behavior as well as the small dimension of the microdischarges. Microdischarges at atmospheric pressure conditions can leave similar erosion traces on metallic films (Al, Ti) as PEO microdischarges on oxide films, and possibly can support a better understanding of the plasma-solid-interactions as well as microdischarge characteristics during PEO. A porous aluminum oxide film is deposited on aluminum substrates by pre-anodizing at a voltage of 250 V and is treated afterwards with a relative short (duration of 1 min) PEO process at a voltage of about 500 V or filamentary dielectric barrier discharges, namely a self-organized Dielectric Barrier Discharge (DBD) and a DBD-like plasma jet operated both with a He/N2 (95%/5%) gas flow. The gas temperature at DBD plasma conditions, measured using the rotational distribution in the emission spectra of molecular nitrogen, is low and amounts to about 400 K. Erosion traces on the surface of the oxide film caused by PEO and plasma spots of both atmospheric pressure discharges are studied by scanning electron microscopy and energy dispersed x-ray spectroscopy. Form and dimensions of erosion traces and established modifications of the material composition generated by the treatment with these DBD microdischarges under atmospheric pressure conditions are similar to those ones generated by the PEO process. Hence, a similar mechanism of these processes is supposed. For stronger evidences of the assumed PEO mechanism additional experimental studies are needed.

Fourier‐transform infrared spectroscopy of ethyl lactate decomposition and thin‐film coating in a filamentary and a glow dielectric barrier discharge

AbstractGlow and filamentary regimes of atmospheric pressure plasma‐enhanced chemical vapor deposition in a planar dielectric barrier discharge configuration were compared for thin‐film deposition from ethyl lactate (EL). EL decomposition in the plasma phase and thin‐film composition were both characterized by Fourier‐transform infrared spectroscopy. EL chemical bonds' concentration along the gas flow decreases progressively in the glow dielectric barrier discharge (GDBD), whereas it drastically oscillates in the filamentary dielectric barrier discharge (FDBD), with values higher than that of the initial mixture. EL decomposition route depends on the discharge regime, as the decrease of the concentration of the different investigated bonds is different for an identical amount of energy provided to EL molecules. CO2 is systematically formed reaching concentrations of 25 and 40 ppm, respectively, in FDBD and GDBD.

Nonlinear feature in the spatial uniformity of an atmospheric helium dielectric barrier discharge with the inter-dielectric gap width enlarged

Intuitively, when the breakdown voltage is satisfied, enlarging the inter-dielectric gap width (d g) is prone to filamentary dielectric barrier discharges (DBDs) due to the lengthened electron migration path and the intensified electron cascade. In this letter, we report that in specific conditions, a larger d g can also promote a homogeneous DBD. The calculated results from the two-dimensional fluid model of an atmospheric helium DBD reveal that the incomplete dissipation of glows (residual positive column) induced by the enlarged d g poses an eraser-like role, wiping out the surface charges left behind by the former discharge. Thus, the so-called memory effect cannot be well established, and the uniform DBD ensues. An experiment with similar conditions and a simplified linear stability analysis qualitatively validate the calculated results. This work also provides sufficient feasibility of regulating discharge uniformity of DBDs through manipulating the dissipative characteristic, and some methods of tailoring waveform would be useful.

Reconfigurable plasma photonic crystals from triangular lattice to square lattice in dielectric barrier discharge

We demonstrate a flexible experimental method to realize fast reconfiguration of plasma photonic crystals by self-organization of filaments in dielectric barrier discharge (DBD). The symmetry and lattice constant of plasma photonic crystals can both be dynamically tuned by simply changing the applied voltage. The reconfiguration from a triangular lattice to a square lattice is realized and the triangular lattices with different lattice constants are also obtained. A phenomenological reaction-diffusion model of two interacting layers is established to simulate the formation of different plasma structures. Experimental observations and numerical simulation are in good agreement. Moreover, the band diagrams of different plasma photonic crystals have been studied by use of finite element method. It is shown that the positions and sizes of the band gaps change significantly when the configurations of plasma photonic crystals have been changed. Such plasma structures can be used as potential tunable metamaterials, which may find wide applications in the manipulation of microwaves and terahertz waves.

NOx synthesis by atmospheric‐pressure N2/O2 filamentary DBD plasma over water: Physicochemical mechanisms of plasma–liquid interactions

AbstractIn this study, an atmospheric‐pressure filamentary dielectric barrier discharge plasma is produced over a deionized (DI) water surface to study the physicochemical mechanisms of plasma–liquid surface interactions for NOx synthesis. The gas‐phase plasma diagnostics are performed using optical emission spectroscopy, Fourier‐transform infrared spectroscopy, and by recording voltage–current curves, and liquid‐phase species are analyzed using ion chromatography and UV−visible spectrophotometer. The investigations indicate that the reaction pathways for reactive oxygen and nitrogen species (H2O2, , ) formation in DI water depend on different experimental conditions. It is observed that the conversion of nitrites into nitrates is significantly influenced by reactive oxygen species. The energy yield for the total amount of NOx synthesized ranges from 1.3 × 10−4 to 3.4 × 10−3 mol/MJ.

Development and Optimization of Single Filament Plasma Jets for Wastewater Decontamination

New efficient depollution techniques for water decontamination, purification and disinfection are being sought to replace those classic methods (chemical, filtration, ozonisation, photochemical reactions) that have deficiency for some substances. The use of plasma technologies, discharges in, or in contact with, wastewater are promising approaches for the decomposition of pollutants by highly oxidative radicals, charged particles, UV radiation, etc. produced by plasma. In the present study we report on the potential of radiofrequency single and multiple filamentary Dielectric Barrier Discharge (DBD) jets for the decolorization of methylene blue (MB) dye in water solutions. Optical emission spectroscopy (OES) investigations were performed for the characterization of plasma evolving in air, and in liquid. The decolorization process was monitored by absorption spectroscopy. We determined the decolorization time, according to a variety of external parameters. The key parameters for obtaining the maximum decolorization rate were identified as being the discharge tube diameter, tube nature (glass/ceramic), the injected power in the discharge, the type of reactive gas and the number of filamentary plasma jets.

Atmospheric pressure self-organized filaments in dielectric barrier discharge excited by a modulated sinusoidal voltage

Excited by a modulated sinusoidal voltage, self-organized filaments are generated in a parallel plate dielectric barrier discharge with a flowing mixture of argon and nitrogen at atmospheric pressure. With increasing off time of the modulated voltage, a single filament transits into a pair of filaments. Then, the self-organized filaments undergo a scenario from triangle, quadrilateral, pentagon, hexagon, and finally, to a ring composed of rotating filaments. During the transition process, the discharge current always presents a single pulse per half voltage cycle, whose amplitude increases for both positive and negative discharges. However, discharge current symmetry deteriorates. Moreover, with increasing off time, the inception voltage increases for the positive discharge, while it decreases for the negative discharge. For the hexagonal arranged filaments, temporal evolutions are implemented for the positive and negative discharges. The results reveal that the initiation in one current pulse seems to propagate opposite to the gas flow direction in the positive discharge, while advances along it in the negative discharge. By optical emission spectroscopy, the electron temperature and electron density are investigated via Boltzmann plotting and a line ratio from 738 nm to 750 nm, respectively. With increasing off time, both of them increase for the positive discharge, while they decrease for the negative discharge. What is more, both electron temperature and electron density increase as the inception voltage increases.

Effect of airflow on the space-time distribution of filaments in dielectric barrier discharge at atmospheric pressure

The effect of flowing air on dielectric barrier discharge excited by alternating voltage was investigated by high-speed video analysis and electrical measurements. The discharge was still in filamentary mode in flowing air, and the space-time distribution of filaments was changed by airflow. With the increase in airflow velocity, the space-time distribution of discharge filaments shown in top view images went through four phases, that is, spot-like distribution, line-like distribution, cotton-like distribution, and stripe-like distribution. Accordingly, the motion and morphology of discharge filaments shown in side view images also presented four phases: remaining still and straight between adjacent cycles, moving and bending downstream, almost remaining still and straight between adjacent cycles, and moving and bending downstream again. Different motions of filaments were considered to be the reason for the changed distribution of filaments in flowing air. In addition, the intensity of discharge in flowing air was enhanced by increasing the gas gap and discharge frequency. At high discharge current, larger airflow velocity was needed to reach phase transition. The changed distribution of micro-discharge remnants in flowing air can be responsible for the phase transition. Micro-discharge remnants redistributed during the time interval of adjacent half-cycle discharges, under the action of various forces, such as electric field force, drag force, repulsive force, electrostatic coupling force, and trap binding force. The changed position of micro-discharge remnants led to the complex motions of discharge filaments and further resulted in the changed space-time distribution of filaments.

Electrical modelling of homogeneous and filamentary dielectric barrier discharge at atmospheric pressure

Abstract An electrical model of Dielectric Barrier Discharge (DBD) is proposed to model the homogeneous and filamentary discharge. In the first part, for the homogeneous discharge, an equivalent circuit based on the electrical behaviour of DBD is studied. The discharge current and the gap voltage signals are given as a result of model simulation. The analysis of charge transfer has been carried out by means of Lissajous figures, and the dynamic of the discharge is depicted by the discharge characteristic. In the second part, for the filamentary discharge, the randomness of streamers breakdowns and the high frequency of the current pulses have been modelled based on a statistical study of breakdowns distribution. The results of the simulation for the two modes of discharge will be compared to the experimental outcomes.

Filamentary nanosecond surface dielectric barrier discharge. Experimental comparison of the streamer-to-filament transition for positive and negative polarities

Streamer-to-filament transition is a general feature of high pressure high voltage nanosecond surface dielectric barrier discharges (nSDBDs) for mixtures containing molecular gases. The transition is observed at high pressures and voltages in a single-shot experiment a few nanoseconds after the start of the discharge. A set of experimental results comparing streamer-to-filament transition and properties of plasma in the filaments for the identical high voltage pulses of negative and positive polarity is presented. The transition curves in voltage–pressure coordinates are obtained for N2:O2 mixtures with different content of molecular oxygen, from 0% to 20%, at the pressure range 1–12 bar. Continuous optical spectra are compared for both polarities in 6 bar synthetic air. Electron density is calculated from Stark broadening of Hα line at λ = 656.3 nm in the discharge and in early afterglow, 40 nanoseconds after the end of the high voltage pulse. Hydrodynamic perturbations are measured using schlieren imaging in 1–6 bar air for streamer and filamentary mode for both polarities. The review of common and distinctive features of the filamentary single-shot nSDBD for two polarities of the applied pulse is provided.

Use of pre-ionization electrodes to produce large-volume, densely distributed filamentary dielectric barrier discharges for materials surface processing

Scaling up atmospheric pressure dielectric barrier discharges is a challenging prerequisite to expanding their industrial applications. In this study, we present the results of large-volume dielectric barrier discharges (DBDs) with a parallel plate electrode configuration having an electrode surface of 50 × 200 mm2 and an interelectrode gap of 5 mm. Highly dense filamentary DBD plasma was stably generated over a large area using pre-ionization electrodes embedded in the one of electrodes. We show that the role of the pre-triggering system is crucial in producing a densely distributed filamentary discharge over the electrode surface, especially at the main discharge voltage values of 14.0–18.0 kVp-p and pre-ionization voltage of 7.0–10.0 kVp-p at the same frequency, ranging from 1 to 4 kHz. By tuning the phase difference between the pre-ionization and main discharge voltages to around 180 degrees, both discharge current amplitude and duration time per period of main DBDs are maximized. The present results indicate that such a large-volume DBD is extremely versatile and suited for a wide range of industrial applications.

Synthesis of diamond-like hydrocarbon films by atmospheric pressure filamentary dielectric barrier discharge

Diamond-like hydrocarbon (DLHC, a-C:H) films were synthesized under atmospheric pressure filamentary by dielectric discharge (FDBD) to improve their mechanical properties compared to the films synthesized by glow dielectric barrier discharge (GDBD). GDBD is generally used for atmospheric pressure-plasma-enhanced chemical vapour deposition. The discharge form transitioned from GDBD to FDBD by increasing the gap between electrodes from 1 to 4 mm. The hardness of the films increased from 3.7 to 11.9 GPa by using FDBD. The results indicate that hard DLHC films can be synthesized at room temperature and on a large area under atmospheric pressure using FDBD.

Conference Proceedingon Nanomaterials and Nanochemistry Hard Carbon and Silica based Films Synthesized under Atmospheric Pressure

Atmospheric pressure-plasma enhanced chemical vapor deposition (AP-PECVD) method using a dielectric barrier discharge (DBD)is a cost-effective process because of no need of vacuum process. In this study, we synthesized silicabased films (SiO:CH) and hydrogenated amorphous carbon films (A-C:H) by AP-PECVD method. We synthesized SiO:CH films from tetramethoxysilane (TMOS) and O2 diluted with N2 and investigated the effect of the substrate temperature and the TMOS flow rate on hardness of the films. The hardness increased from 4.0 to 6.9 GPa as the substrate temperature increased from 80 to 300°C. To synthesize a-C:H films, filamentary DBD (FDBD) was used to improve the hardness compared to the films synthesized by glow DBD (GDBD), which is generally used for APCVD.The hardness of the films increased from 3.7 to 11.9 GPa by using FDBD.