Homogeneous Dielectric Barrier Discharge Research Articles

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.

Modelling of Nonthermal Dielectric Barrier Discharge Plasma at Atmospheric Pressure and Role of Produced Reactive Species in Surface Polymer Microbial Purification

A nonthermal atmospheric plasma reactor was used to sterilize polymer surfaces and satisfy safety constraints in a biological medium. A 1D fluid model was developed using COMSOL Multiphysics software® 5.4 with a helium-oxygen mixture at low temperature for the decontamination of bacteria on polymer surfaces. An analysis of the evolution of the homogeneous dielectric barrier discharge (DBD) was carried out through studying the dynamic behavior of the discharge parameters including the discharge current, the consumed power, the gas gap voltage, and transport charges. In addition, the electrical characteristics of a homogeneous DBD under different operating conditions were studied. The results shown that increasing voltage or frequency caused higher ionization levels and maximum increase of metastable species' density and expanded the sterilization area. On the other hand, it was possible to operate plasma discharges at a low voltage and a high density of plasma using higher values of the secondary emission coefficient or permittivity of the dielectric barrier materials. When the discharge gas pressure increased, the current discharges declined, which indicated a lower sterilization efficiency under high pressure. A short gap width and the admixture of oxygen were needed for sufficient bio-decontamination. Plasma-based pollutant degradation devices could therefore benefit from these results.

Realization of homogeneous dielectric barrier discharge in atmospheric pressure argon and the effect of beads on its characteristics

This paper describes the realization of a homogeneous dielectric barrier discharge (DBD) in argon at atmospheric pressure. The effect of the morphology of the dielectric surface (especially the dielectric surface covered by hollow ceramic beads (99% Al2O3) with different diameters) on discharge is investigated. With different dielectrics, the argon DBD presents two discharge modes: a filamentary mode and a homogeneous mode. Fast photography shows that the filamentary mode operates in a streamer discharge, and the homogeneous mode operates in a Townsend discharge regime. It is found that a homogeneous discharge can be generated within a certain voltage range. The voltage amplitude range decreases, and the breakdown voltage increases with the increase in the mean diameter of the ceramic beads. Waveforms of the total current and optical emission signal present stochastic pulses per half voltage cycle for the filamentary mode, whereas there is one single hump per half voltage cycle for the homogeneous mode. In the homogeneous mode, the intensity of the optical emission decreases with the mean diameter of the ceramic beads. The optical emission spectrum is mainly composed of atomic lines of argon and the second positive system of molecular nitrogen. It reveals that the electron density decreases with the increasing mean diameter of the ceramic beads. The vibrational temperature increases with the increasing mean diameter of the ceramic beads. It is believed that a large number of microdischarges are formed, and smaller ceramic beads have a larger activation surface area and more point discharge. Electrons liberated in the shallow well and electrons generated from microdischarges can increase the secondary electron emission coefficient of the cathode and provide initial electrons for discharge continuously. Therefore, the breakdown electric field is reduced, which contributes to easier generation of homogeneous discharge. This is confirmed by the simulation results.

Pre-breakdown to stable phase and origin of multiple current pulses in argon dielectric barrier discharge

We report on the results of numerical models of the (i) initial growth and (ii) steady state phases of atmospheric-pressure homogeneous dielectric barrier discharge in argon. We employ our new in-house code called PyDBD, which solves continuity equations for both particles and energy, shows exceptional stability, is accelerated by adaptive time stepping and is openly available to the scientific community. Modeling argon plasma is numerically challenging due to the lower speeds of more inertial ions compared to more commonly modeled neon and helium, but its common use for plasma jets in medicine makes its modeling compelling. PyDBD is here applied to modeling two setups: (i) the exponential growth from natural electron-ion seeds (onset phase) until saturation is reached and (ii) the multiple current pulses that naturally appear during the steady state phase. We find that the time required for the onset phase, when the plasma density grows from 109 m−3 to 1017 m−3, varies from 80 μs at 4.5 kV down to a few μs above 6.5 kV, for voltage frequency f = 80 kHz and gap width d g = 0.9 mm. At the steady state, our model reproduces two previously observed features of the current in dielectric barrier discharge reactors: (1) an oscillatory behavior associated to the capacitative character of the circuit and (2) several (N p) current pulses occurring every half sinusoidal cycle. We show that the oscillations are present during the exponential growth, while current pulses appear approaching the steady state. After each micro-discharge, the gas voltage decreases abruptly and charged particles rapidly accumulate at the dielectric boundaries, causing avalanches of charged particles near the reactor boundaries. Finally, we run a parametric study finding that N p increases linearly with voltage amplitude V amp, is inversely proportional to dielectric gap d g and decreases when voltage frequency f increases. The code developed for this publication is freely available at the address https://github.com/gabersyd/PyDBD.

Influence of Ti3C2T x (MXene) on the generation of dielectric barrier discharge in air

The formation of homogeneous dielectric barrier discharge (DBD) in air is a key scientific problem and core technical problem to be solved for the application of plasmas. Here, we report the effect of two-dimensional (2D) nanomaterial Ti3C2T x (T x = –F, –O and/or –OH) on regulating the electrical discharge characteristics. The field emission and weak bound state property of Ti3C2T x can effectively increase the seed electrons and contribute to the generation of atmospheric pressure homogeneous air DBD. The electron avalanche development for the uneven electrode structure is calculated, and the discharge mode transition is modeled. The comparative analyses of discharge phenomena validate the regulation of Ti3C2T x on the discharge characteristics of DBD. The light emission capture and the voltage and current waveforms verify that the transition of Townsend discharge to streamer discharge is effectively inhibited. The optical emission spectra are used to characterize the plasma and confirm that it is in a non-equilibrium state and the gas temperature is at room temperature. This is the first exploration of Ti3C2T x on the regulation of electrical discharge characteristics as far as we know. This work proves the feasibility of Ti3C2T x as a source of seed electrons to form homogeneous DBD, establishing a preliminary foundation for promoting the application of atmospheric pressure non-equilibrium plasma.

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.

Theoretical Kinetics Investigation of Krypton Dielectric Barrier Discharge for UV Lamp

This work presents an electric and kinetic study of homogeneous dielectric barrier discharge (DBD) in pure krypton (Kr). The electrical characterization and kinetic analyses of the DBD in Kr are performed. The plasma formation in DBD, excited by sinusoidal voltage at high pressure, was studied. The discharge development, with homogeneous model approach and using extended kinetic scheme, is simulated. The study is based on a spatial homogeneity model including the plasma chemistry, the electrical circuit and the Boltzmann equations’. The temporal variations of discharge voltage, dielectrics voltage, discharge current, electric field and species concentrations are calculated. The plasma kinetics is discussed with the aim to finding the optimal efficiency. The photon generation, under typical operating conditions, was investigated and discussed. The effect of some parameters on the excilamp like pressure, applied voltage, and frequency are investigated in order to identify the optimal parameters for maximum luminous efficiency in the UV range.

Influence of Oxygen on the Multiple-Current-Pulse Behavior in an Atmospheric Homogeneous Helium Dielectric Barrier Discharge With Air Impurities

In this paper, through a one-dimensional fluid model, we investigate the influence of oxygen on the multiple-current-pulse (MCP) behavior in an atmospheric homogeneous dielectric barrier discharge (HDBD) in helium with air impurities. From the simulation results, we find that the O2 Penning ionization plays a leading role in the discharge characteristics. As the air content increases from 0 ppm to 5000 ppm, the current waveforms show a transition from a single-pulse mode to MCP mode, and the number of current pulses ( $N_{\mathrm {p}}$ ) also increases. Through analysis, we find that although $N_{\mathrm {p}}$ increases monotonically, the evolution mechanism of the MCP discharges under different ranges of air content is different. At lower air concentration (less than 500 ppm here), we find the similar explanation as that reported in our previous work on the MCP behavior only considering N2 impurity. However, when the air content is higher, we find that the seed electron density ( $n_{\mathrm {e0}}$ ) remains basically unchanged, not like the sharp drop at lower air concentration. Further analysis reveals that the rapid growth of direct ionization during a small period before the breakdown helps generate MCP discharges. In addition, the attachment reaction of O2 is analyzed. Results show that at higher air content (above 5000 ppm here), the O2 attachment reaction will provide more possibilities of successive ignitions after the first pulse with the assistance of the applied voltage, implying a stimulative effect of the oxygen on MCP discharges.

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.

Influence of nitrogen impurities on the performance of multiple-current-pulse behavior in a homogeneous helium dielectric-barrier discharge at atmospheric pressure

A systematic investigation regarding the influence of nitrogen impurities on the evolution of multiple-current-pulse (MCP) behavior in a homogeneous dielectric-barrier discharge is carried out via fluid modelling. By gradually up-regulating the N2 content from 0.1 ppm to 10 000 ppm, the discharge evolves from MCP mode into a single-pulse mode, and finally returns to MCP mode. Analyses reveal that Penning ionization plays an important role in regulating the MCP performance. Under 10 ppm nitrogen content, the direct electron impact ionization predominates the total ionization process while Penning ionization is negligible. A relatively low pre-ionization level and seed electron level of incipient pulse (ne0) in this stage induce a strong incipient current pulse as well as MCP. As N2 content increases, the pre-ionization level and ne0 are enhanced due to the elevation of Penning ionization rate, leading to the smoothing of gap voltage profile and the annihilation of MCP at 10 ppm. Above 100 ppm, Penning ionization becomes the dominant ionization channel. As N2 content exceeds 300 ppm, the MCP reappears, which is believed to be resulted from a slump in metastable density owing to the excessive dissipation by Penning ionization. Beyond 1000 ppm, the strengthening of glow discharge structure at the incipient current peak phase contributes to the further increase of Jpm as well as pulse number.

Homogeneous dielectric barrier discharges in atmospheric air and its influencing factor

The stable homogeneous dielectric barrier discharge (DBD) is obtained in atmospheric 2–3 mm air gap. It is generated using center frequency 1 kHz high voltage power supply between two plane parallel electrodes with specific alumina ceramic plates as the dielectric barriers. The discharge characteristics are studied by a measurement of its electrical discharge parameters and observation of its light emission phenomena. The results show that a large single current pulse of about 200 μs duration appearing in each voltage pulse, and its light emission is radially homogeneous and covers the entire surface of the two electrodes. The homogeneous discharge generated is a Townsend discharge during discharge. The influences of applied barrier, its thickness, and surface roughness on the transition of discharge modes are studied. The results show that it is difficult to produce a homogeneous discharge using smooth plates or alumina plate surface roughness Ra < 100 nm even at a 1 mm air gap. If the alumina plate is too thin, the discharge also transits to filamentary discharge. If it is too thick, the discharge is too weak to observe. With the increase of air gap distance and applied voltage, the discharge can also transit from a homogeneous mode to a filamentary mode. In order to generate stable and homogeneous DBD at a larger air gap, proper dielectric material, dielectric thickness, and dielectric surface roughness should be used, and proper applied voltage amplitude and frequency should also be used.

Numerical investigation on the dynamics and evolution mechanisms of multiple-current-pulse behavior in homogeneous helium dielectric-barrier discharges at atmospheric pressure

A systematic investigation on the dynamics and evolution mechanisms of multiple-current-pulse (MCP) behavior in homogeneous dielectric barrier discharge (HDBD) is carried out via fluid modelling. Inspecting the simulation results, two typical discharge regimes, namely the MCP-Townsend regime and MCP-glow regime, are found prevailing in MCP discharges, each with distinctive electrical and dynamic properties. Moreover, the evolution of MCP behavior with external parameters altering are illustrated and explicitly discussed. It is revealed that the discharge undergoes some different stages as external parameters vary, and the discharge in each stage follows a series of distinctive pattern in morphological characteristics and evolution trends. Among those stages, the pulse number per half cycle is perceived to observe non-monotonic variations with applied voltage amplitude (Vam) and gap width (dg) increasing, and a merging effect among pulses, mainly induced by the enhanced contribution of sinusoidal component to the total current, is considered responsible for such phenomenon. The variation of incipient discharge peak phase (Φpm) is dominated by the value of Vam as well as the proportion of total applied voltage that drops across the gas gap. Moreover, an abnormal, dramatic elevation in Jpm with dg increasing is observed, which could be evinced by the strengthened glow discharge structure and therefore enhanced space charge effect.

A compact nanosecond pulse generator for DBD tube characterization.

High voltage pulses of very short duration and fast rise time are required for generating uniform and diffuse plasma under various operating conditions. Dielectric Barrier Discharge (DBD) has been generated by high voltage pulses of short duration and fast rise time to produce diffuse plasma in the discharge gap. The high voltage pulse power generators have been chosen according to the requirement for the DBD applications. In this paper, a compact solid-state unipolar pulse generator has been constructed for characterization of DBD plasma. This pulsar is designed to provide repetitive pulses of 315 ns pulse width, pulse amplitude up to 5 kV, and frequency variation up to 10 kHz. The amplitude of the output pulse depends on the dc input voltage. The output frequency has been varied by changing the trigger pulse frequency. The pulsar is capable of generating pulses of positive or negative polarity by changing the polarity of pulse transformer's secondary. Uniform and stable homogeneous dielectric barrier discharge plasma has been produced successfully in a xenon DBD tube at 400-mbar pressure using the developed high voltage pulse generator.

Numerical investigation of Ar–NH3 mixture in homogenous DBDs

In this paper, a study of homogenous dielectric barrier discharge Ar–NH3 was made in order to investigate the electrical and the physical characteristics of homogenous discharge at atmospheric pressure. The discharge model includes the electrical module and the chemical kinetic module. The results obtained by the present model were compared with experimental work. The evolution of the plasmas voltage, the species densities, and the concentration of charged species are analyzed and discussed.

Research on Homogeneous Multilayer DBD Driven by Submicrosecond Pulsed Power at Atmospheric Pressure Air

Multilayer dielectric barrier discharge (DBD) can efficiently enlarge the volume of homogeneous plasma and its interactional surface area with materials in vertical space, which seems attractive to the industry application. In this paper, a new plasma generator of DBD structure which has multilayers of dielectric barrier boards excited by repetitive submicrosecond pulsed power (0 to −100 kV, 130 Hz–1 kHz, pulsewidth 230 ns, and rise time 120 ns) is introduced, and homogeneous plasma has been obtained in atmospheric pressure air. Experiments on high-speed photography with an exposure time of 5 ns have been carried out to the discharge with three layers of dielectric barrier boards with each gap width of 2 mm. It demonstrates that luminance of the discharge distributes uniformly throughout the upper and the lower gaps. Also, the result of the time evolution image of a three-layer DBD is discussed in this paper, which shows that the two layers of luminous intensity keep good consistency with each other, and this indicates that breakdown of each gap layer happens at the same time in a multilayer DBD. A preliminary processing experiment for polytetrafluoroethylene film has been carried out by adopting homogeneous triple-layer DBD plasma. By testing the water contact angle of the polymer surface before and after the treatment, it was found that hydrophilism of the surface and efficiency of treatment could be effectively improved by the processing of each layer of discharge plasma.

Generation of atmospheric-pressure homogeneous dielectric barrier discharge in air

To generate an atmospheric-pressure homogeneous dielectric barrier discharge (APHDBD) in air, a line-plane electrode with a floating-voltage electrode, which consists of a high-voltage electrode, floating-voltage electrode, air-gap, barrier dielectric, and metal electrode, is proposed. Studies of the electric field of the line-plane electrode with a floating-voltage electrode show that strong electric field areas beneficial for generating initial discharges are formed near the contact point between the high-voltage electrode and the floating-voltage electrode. These areas can provide sufficient and evenly distributed initial electrons for the air-gap with relatively uniform and low electric fields. Thus, a filamentary discharge in the air-gap can be inhibited. Experiments show that the floating-voltage electrode makes it easy to reduce the initial discharge voltage and improve the uniformity of discharge. When the air-gap is 2–8 mm, the discharge occurs in the APHDBD mode, and when it is 9 mm, it changes from diffuse-like to corona discharge.

Influence of the Discharge Mode on the Optical and Passivation Properties of SiNx:H Deposited by PECVD at Atmospheric Pressure

The cost of industrial silicon solar cells could be greatly reduced by the implementation of PECVD at atmospheric pressure for the deposition of the silicon nitride (SiN) antireflective coating. For a successful development of this vacuum-free process tool, a deep understanding of the plasma discharge mode has to be undertaken. This work focuses on the control of a wide range of plasma excitation conditions in order to obtain homogeneous dielectric barrier discharges (DBD) at atmospheric pressure, and thus dense and uniform SiN layers. The influence of the discharge mode is then studied in order to optimize the optical and passivation properties of the SiN thin films, showing good antireflective properties as well as surface recombination velocities as low as 15cm.s-1.

Atmospheric Pressure Radio‐Frequency DBD Deposition of Dense Silicon Dioxide Thin Film

Radio‐frequency (RF) homogeneous dielectric barrier discharge (DBD) is compared to low frequency glow DBD to make silicon oxide from Ar/NH3/SiH4. RF‐DBD is a more powerful discharge, and the growth rate is not limited by precursor dissociation rate but by powder formation. Powders are not deposited in the plasma zone but in the post‐discharge due to their trapping by the electric field. Modulation of the RF‐DBD is a useful solution to avoid powder formation. Powders are systematically avoided if the plasma energy during time on stays below 750 µJ. RF‐DBD modulation also increases the growth rate twofold compare to continuous RF. The optimum growth rate without powder corresponds to a short Ton to limit precursor dissociation, a long Toff to enhance diffusion and a fast repeat frequency to increase deposition rate.

Transition from Townsend to radio-frequency homogeneous dielectric barrier discharge in a roll-to-roll configuration

The aim of this paper is to better understand the transition from Townsend to radio-frequency homogeneous dielectric barrier discharge (DBD) at atmospheric pressure. The study is done in an Ar/NH3 Penning mixture for an electrode configuration adapted to roll-to-roll plasma surface treatment. The study was led in a frequency range running from 50 kHz up to 8.3 MHz leading to different DBD modes with a 1 mm gas gap: Glow (GDBD), Townsend (TDBD), and Radio-frequency (RF-DBD). In the frequency range between TDBD and RF-DBD, from 250 kHz to 2.3 MHz, additional discharges are observed outside the inter-electrode gas gap. Because each high voltage electrode are inside a dielectric barrel, these additional discharges occur on the side of the barrel where the gap is larger. They disappear when the RF-DBD mode is attained in the 1 mm inter-electrode gas gap, i.e., for frequencies equal or higher than 3 MHz. Fast imaging and optical emission spectroscopy show that the additional discharges are radio-frequency DBDs while the inter-electrode discharge is a TDBD. The RF-DBD discharge mode is attained when electrons drift becomes low enough compared to the voltage oscillation frequency to limit electron loss at the anode. To check that the additional discharges are due to a larger gas gap and a lower voltage amplitude, the TDBD/RF-DBD transition is investigated as a function of the gas gap and the applied voltage frequency and amplitude. Results show that the increase in the frequency at constant gas gap or in the gas gap at constant frequency allows to obtain RF-DBD instead of TDBD. At low frequency and large gap, the increase in the applied voltage allows RF-DBD/TDBD transition. As a consequence, an electrode configuration allowing different gap values is a solution to successively have different discharge modes with the same applied voltage.

Time-resolved spectroscopy of a homogeneous dielectric barrier discharge for soft ionization driven by square wave high voltage

Helium capillary dielectric barrier discharge driven by the square wave-shaped high voltage was investigated spatially and temporally by means of optical emission spectroscopy. The finding of the previous investigation conducted with the sinusoidal-like high voltage was confirmed, i.e., the plasma in the jet and the plasma in the capillary constitute two temporally separated events. The plasma in the jet occurs prior to the discharge in the capillary and exists only during the positive half period of the applied high voltage. The time delay of the capillary discharge with respect to the discharge in the jet depended on the high voltage, and it was between 2.4 and 8.4μs for the voltage amplitude change in the range from 1.96 to 2.31kV, respectively. It was found that, compared to sinusoidal-like voltage, application of the square wave high voltage results with stronger (~6 times) He line emission in the jet, which makes the latter more favorable for efficient soft ionization. The use of the square wave high voltage enabled comparison of the currents (~1mA) flowing in the capillary during the positive and negative high voltage periods, which yielded the estimation for the charge dissipated in the atmosphere ((4 ± 20%) × 10(-11)C) through the plasma jet.