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The experiment of dielectric barrier discharge in a 2 mm air gap shows that the pressure range of a uniform discharge using polytetrafluoroethylene as barrier is much wider than that using quartz or alumina. The parameters of the charge trapped on the surface of these three dielectric barriers were obtained by surface charge measurement and thermal...
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... the charge on the surface could be calculated with the measured . 8 In the experiment, the tested dielectric plate is exposed to the corona discharge produced around the needle electrode powered by a negative voltage of 5 kV for 10 s, and then the needle electrode was quickly removed and replaced by a probe with an effective area of 0. 44 Fig. 4 in which every data point on each curve is an average over three measurements. Since the reproducibility was quite good with a maximum deviation of 0.03 pQ/ mm 2 , the error bars were too small to be marked on the curves. The limitation of the method comes from the sensitivity of the method, i.e., the corona discharge should be able to ...Context 2
... highest pressure at which a uniform DBD could be produced for three tested dielectrics is quite different, 35 kPa for PTFE, 10 kPa for quartz, and 6 kPa for alumina. The reason for this difference most possibly lies in the remarkable differences in their trapping parameters. For PTFE, the value of the initially trapped surface charge, as shown in Fig. 4, is high and decays very slowly. Furthermore, a large amount of the surface charge are trapped in the shallow trap of 0.37 eV, that are easy to be removed from the dielectric surface, providing many seed electrons necessary for uniform discharge and leading to a widest pressure range of the uniform discharge among these three tested ...Context 3
... necessary for uniform discharge and leading to a widest pressure range of the uniform discharge among these three tested dielectrics. It is important to compare the results of alumina and quartz. Although the initially trapped surface charge of alumina is much higher than that of quartz, it decays much faster than that quartz, as shown in Fig. 4. Moreover, in contrast to alumina that has no trap center in low energy band, quartz has a trap center of 0.5 eV from which the surface charge is easier to be released. That is why quartz has a wider pressure range of the uniform discharge than ...Similar publications
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The discharge was driven in an amplitude-modulated regime with a driving AC frequency of 1kHz, va...
Nanosecond-pulse surface dielectric barrier discharge is a promising method used for airflow control application. In our letter, atmospheric-pressure plasmas in open air are produced in a configuration of discharge actuators by repetitive nanosecond pulses. The electrical parameters including applied voltage, total discharge current, and transporte...
Citations
... Fundamental principles and measurement procedures of the ISPD method have been extensively discussed [38]. In the present ISPD method, trap centers were assumed uniformly distributed and only two types of surface trap were identified, i.e. shallow and deep traps with different energies [39,40]. The hopping probability of electrons is higher and the migration period is shorter for shallow traps due to lower barrier heights. ...
Positive streamer behaviors under repetitive pulses are predominantly dependent on the availability of free electrons. If surface residual electrons stored from previous discharges could be intentionally released and involved into the next discharge, an alternative control freedom is provided apart from voltage waveform tailoring methods that mainly attract or repel gaseous residual charges. Evolutions of repetitively pulsed surface streamers in compressed (0.2 MPa) air were investigated after low-photon-energy pulsed visible (532 nm) and infrared (1064 nm) laser irradiations. Pulse-sequence and temporally resolved diagnostics were implemented to investigate effects of laser parameters (irradiation moment, wavelength, energy) and gas composition. A 2D surface streamer fluid simulation was performed to qualitatively unveil impacts of localized plasma patches. The surface streamer morphology and emission light are significantly and repeatably affected by the laser irradiation before the streamer inception, while, variations totally disappear without the solid surface. The secondary streamer is prolonged accompanied by a higher flashover probability after the pulsed laser irradiation in compressed air. Intriguingly, influences of the infrared laser persist for tens of microseconds before the next voltage pulse. Residual charge dynamics under the laser irradiation are analyzed, where the additional increase of O2− of low electron bound energy is emphasized. The laser induced surface trapped electron desorption is achieved through the direct or the step-wise process, dependent on the laser energy and the surface trap state distribution.
... In 2008, Li et al. [64] studied the effect of different dielectric materials on DBD at reduced pressure air plasma. They used polytetrafluoroethylene (PTFE), quartz, and Al 2 O 3 as dielectric plates and found that the pressure range for generating H-DBD was wider when using PTFE as the barrier. ...
... To better F I G U R E 1 The results of the surface charge measurement. 2.5 mm air needle-plane geometry gap with a negative voltage of 5 kV corona discharge for 10 s [64]. ...
... The results of thermally stimulated current measurement. The initial temperature was lowered to 200 K [64]. understand the effect of the mesh electrode, they calculated the electric field distribution in the gap and found that the addition of mesh did not affect the electric field in the discharge. ...
Dielectric 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.
... In literature, this phenomenon is often referred to as 'plasma memory effect'. Long lived negative ions (such as [30,59] or charges stored at the dielectric surface [60] provide initial free electrons for discharge initiation. Once the discharge is initiated, it flows through the easier path created by the residual heat from the previous discharge. ...
This work aims to find how coupled energy per pulse influences the ability of a pulsed dielectric barrier discharge (DBD) plasma to ignite fuel-lean methane-air flow. For that, experiments are performed on a custom-built DBD flow reactor with a variable dielectric thickness and the discharge is operated by bursts of 10 nanosecond duration pulses at 3 kHz repetition rate. With an increase in dielectric thickness, we observe that the coupled energy per pulse decreases even though applied voltage conditions are similar and so more pulses are required to ignite the lean mixture. Interestingly, we observe a significant increase in the minimum ignition energy (M IE) with an increase in the thickness beyond 3 mm. Moreover, the ignition kernel growth rate is much slower in the thicker dielectric cases even though total energy coupling per burst is similar.This phenomenon is investigated further by evaluating plasma parameters using electrical and optical diagnostics. Effective dielectric capacitance, discharge current, and voltage drop across the gas gap are derived from an equivalent circuit analysis, whereas plasma gas temperature and effective reduced electric field (E/N ) are estimated from optical emission spectroscopy. From these analyses, we conclude that a thicker dielectric limits the discharge current and so the plasma filament temperature. For more than 3 mm thick dielectric cases, the filament heating per pulse is too low to achieve strong enough plasma pulse-to-pulse coupling which eventually leads to higher M IE and slower ignition kernel growth rate or the inability to ignite at all.
... This hypothesis was confirmed in later studies. Moreover, it was found [29,30] that electrons adsorbed on the dielectric surface in a DBD can remain there after the plasma exposure for several minutes or even hours. Electron desorption can occur under the photon impact. ...
... The electron is bound with the surface due to the polarization force. In later studies more complicated schemes were considered in terms of shallow energy traps [29] and dielectric energy bands [31]. As to desorption, the thermal mechanism and interaction with excited molecules were estimated to be basic processes in [28]. ...
... As to desorption, the thermal mechanism and interaction with excited molecules were estimated to be basic processes in [28]. Importance of the photodesorption for the DBD operating was first pointed out in [29]. A number of experiments with external irradiation of the dielectric surface by sources of visible or near IR light proved this process existence. ...
The effect of irradiation with visible spectrum light on breakdown in discharge tubes 75–80 cm long and 1.5 cm in inner diameter in rare gases at a pressure of ~1 Torr was studied. A ramp voltage of variable slope in the range of ~10–1–105 kV s-1 was applied to the tube anode. The tube was illuminated by radiation from fluorescent lamps operating in a continuous mode, as well as by LEDs or a laser diode operating in a pulsed mode. The breakdown voltage and the pre-breakdown ionization wave velocity were measured. Illumination led to a change in the breakdown potential. The sign of this change depended on the anode voltage rise rate dU/dt. At dU/dt > 102– 103 kV s-1, the breakdown voltage decreased. A similar effect was observed earlier and was explained by the appearance of electrons in the discharge gap under the light action, as a result of which the breakdown delay time decreased. This, in turn, caused a decrease in the breakdown voltage. At dU/dt < 101–102 kV s-1, on the contrary, the breakdown potential increased; at dU/dt ~ 0.1 kV s-1, this increase could reach 5–6 times. The dependence of the observed effect on the radiation intensity, its wavelength, and the illuminated area position on the tube surface is studied. The pre-breakdown ionization wave behaved in an unusual way under these conditions: its velocity and the signal amplitude recorded by the capacitive probe increased when moving from the high-voltage anode to the cathode. It is assumed that the observed features are caused by the desorbtion of weakly bound electrons from the tube wall surface under the action of irradiation. These electrons create a current that charges the wall near the anode. Since the initial stage of discharge ignition is the initial breakdown between the anode and the tube wall, the anode potential for such a breakdown should increase, which means an increase in the breakdown voltage. Additional experiments with the initiation of a preliminary ionization wave by a pulse applied to the cathode, confirmed the existence of a charge on the wall near the anode.
... The observed pulse-to-pulse coupling in the later discharges is quite similar to our previous work in which we highlighted that pulse-to-pulse coupling can be due to residual heat and charge. Long-living negative ions like O − , O − 2 and charged stored at the dielectric surface can provide free electrons for plasma initiation [2,3,[55][56][57]. Once a discharge is initiated, the residual heat can provide an easier path for the discharge. ...
This work aims to characterize the effects of pulse repetition rate and flow speed on dielectric barrier discharge (DBD) plasma pulse-to-pulse coupling and its ability to ignite methane-air flows. Experiments are performed on a homemade DBD flow reactor with 5 mm discharge gap. Pressure and equivalence ratio are kept constant at 700 mbar and 0.6. First, we perform high-speed intensified imaging to visualize pulse-to-pulse plasma behavior and ignition kernel development. In air flows, plasma morphology changes from multiple weak filaments to a few stronger filaments indicating plasma pulse-to-pulse coupling. This leads to plasma energy addition in nearly the
same gas volume as the previous discharge. The study performed in methane-air flows highlights the importance of plasma pulse-to-pulse coupling for ignition. We find a critical pulse repetition rate and a minimum number of pulses required to achieve a strong enough coupling to develop a successful ignition kernel. Ignition probability and kernel growth are also evaluated for various conditions. Finally, plasma pulse-to-pulse coupling is quantified by measuring the plasma parameters such as gas temperature and reduced electric field from an optical emission spectroscopy.
... Regrading the Townsend second ionization coefficient, some traditional theories believe that the dielectric layer is difficult to generate secondary electrons. However, several studies [29,30] have shown that trapped electrons in the Fig. 9 Cross sections of turn-to-turn insulation model shallow trap on the surface of the barrier dielectric will be considered as secondary electrons during the ion bombardment in general. The Townsend second ionization coefficient is about 0.0025 based on (2). ...
This paper aims to propose a novel data-driven approach for exploring the partial discharge inception voltage (PDIV) of turn-to-turn insulation in inverter-fed motors. To this end, the gas discharge theory-based finite element method is investigated to simulate the state of turn-to-turn insulation, and a comprehensive database is established concerning the structural and environmental factors. Subsequently, a bisected deep belief network (BDBN), which combines with deep belief networks (DBN) and the bisection method, is proposed to explore PDIV. Specifically, DBN is designed to distinguish the discharge state of turn-to-turn insulation, and the testing applied voltage is adaptively adjusted to explore PDIV by the bisection method. The experiment result demonstrates the effectiveness and reliability of BDBN in exploring PDIV of turn-to-turn insulation in terms of precision.
... In the next halfcycle, the polarity was reversed and the alumina became the new temporary cathode, providing more seed electrons by desorbing electrons from the shallow traps. 32 Although the residual space charges might also influence the DBD, this is not significant since the charge decay by recombination of negative-positive ions in atmospheric air (with coefficient of 2 Â 10 À7 cm 3 /s) is generally fast (with characteristic time of 10 ls or less in plasma of density 10 12-16 /cm 3 , shorter than the voltage cycle in the present system). Consequently, in the positive halfcycle, when the alumina electrode acts as the temporary cathode, there are sufficient initial electrons to develop electron avalanches at a relatively low electric field, so that Townsend breakdown is available with a slower, homogeneous discharge. ...
We report in this Letter a kind of asymmetric discharge mode in positive and negative half-cycles of dielectric barrier discharge in ambient air. This phenomenon is characterized by homogeneous and filamentary discharges occurring alternately in the two half-cycles, using two different materials of alumina ceramic and quartz as the dielectric barrier at each side. The discharge current waveforms, discharge images, optical emission spectra, and the averaged electron energy are significantly different for the asymmetric discharges. It is suggested that the seed electrons and secondary electron emission from the different dielectric materials acting as the temporary cathode are responsible for the different discharge modes.
... It indicates that the surface charges play an indispensable role in the ignition and extinguishment of the discharge. In addition, Golubovskii et al [19] and Li et al [20] found that the electron desorption in the dielectric potential well provided extra seed electrons for the next discharge and contributed to the formation of uniform discharge through theoretical simulation and experiment, respectively. Therefore, it is referred that the airflow improves discharge uniformity via modifying the distribution of surface charges. ...
... In fact, it is difficult for the airflow to act directly on the electrons accumulating on the dielectric surface because of the boundary layer effect and the potential wall of the dielectric surface. However, the airflow can act directly on ions in the discharge space, causing them to move towards the outlet of the airflow under the drag force, and drive surface charges to move together through electrostatic force [20]. As a result, the charge decay faster along the dielectric surface in the airflow due to the combination of these two aspects. ...
The surface charges in nanosecond pulsed dielectric barrier discharge (NPDBD) under quiescent air and airflow are detected based on the Pockels effect of electro-optical crystals. In quiescent air, it is found that the surface charge spot propagates and moves in a certain direction due to the combination of the transverse electric field and the thermal accumulation during dozens of consecutive discharge cycles. However, the position of the surface charge spot remains fixed throughout a single discharge cycle (0.83 ms). At the same time, the noticeable decay of surface charges emerges in the above time scales. Furthermore, when the airflow is introduced into the discharge gap, the propagation and movement of surface charges are accelerated. With the increase of airflow velocity, the discharge transforms from a filamentary mode to a diffuse mode, and the distribution of surface charges varies from discrete to uniform. The transition point of the discharge state and charge distribution corresponds to the airflow velocity of 10 m/s. The airflow accelerates the decay of surface charges, resulting in the shrink and dispersion of surface charges, which is considered to be the fundamental reason for the airflow's potential to improve discharge uniformity. The inherent mechanism for achieving uniform discharge is revealed in this study.
... For the studied conditions in this work, electron detachment from negative oxygen ions and electron detrapping from the dielectric surface are the likely dominant mechanisms for providing free electrons. The recombination time of O − 2 and O − can be on the order of milliseconds [49] and quartz can store charge up to several hundreds of seconds [50] . The electrons liberated through these mechanisms can play a crucial role in plasma initiation while the hot channel from a previous discharge can provide an easier path for filament formation. ...
In this work, an experimental study investigating dielectric barrier discharge (DBD) plasma-assisted ignition in methane-air flows at near-atmospheric pressure is presented. Discharges are produced using 10 ns duration high voltage pulses at maximum 3 kHz pulse repetition rate. The goal is to check the feasibility of plasma as an ignition source for ignition-stabilized combustion in a wide range of equivalence ratio, pressure, and flow speed conditions. To that end, four important characteristics are investigated: 1) Ignition dynamics, 2) Minimum number of pulses required for ignition, 3) Plasma energy per pulse, gas temperature, and the effective reduced electric field, and 4) Plasma NOx production. In continuous plasma mode, we observe an elongated flame outside of the discharge region when a methane-air mixture flows through the discharge. The elongated flame is due to repetitively ignited kernels moving downstream with the flow. High-speed intensified imaging is used to explore plasma morphology and ignition dynamics. Plasma has a filamentary nature which is perceived as moving with the flow due to pulse-to-pulse memory effects. For fuel-air mixtures, ignition is followed by kernel expansion and splitting, flame propagation, and consecutive ignition. The time delay between consecutive ignition events is found to be a function of flow speed, because ignition is achieved only when a previously ignited kernel moves out of the plasma region, which happens faster at higher flow speeds. We performed optical emission spectroscopy in burst mode to further characterise plasma and ignition parameters. In air, plasma gas temperature and hence the reduced electric field increases because of pulse-to-pulse effects. By comparing the air plasma temperature with the methane auto-ignition temperature, we conclude that the observed ignition is low-temperature ignition. Parametric studies of NOx measurements suggest that plasma NOx emissions are higher for low flow speeds, high pulse repetition rates, and low-pressure conditions. Overall, our DBD filamentary plasma is found to be a fast, repetitive, and low-temperature ignition source that can be used for ignition-stabilized combustion at near atmospheric conditions.
... Trap energy level represents the ability for bounding charge, while amplitude represents the capacity of bound charge [14]. Detrapping charge under 1 eV could easily change to seed charge of ionization [15]. In 2021, Li summarized a lot of experiments and proposed the U-shaped relation between flashover voltage and surface trap level. ...
Epoxy post-insulator is one of the key parts in SF6 gas-insulated DC wall bushing, which is irreplaceable in HVDC transmission projects. Flashovers occur on post-insulators frequently, where a great number of tiny metal particles exist. The micron metal particles attached to the epoxy will change the insulation state of the surface. However, this relation between microstructure of material and macroscopic electrical properties on flashover would still arouse controversy. In order to study the effect of particles on the flashover characteristics, the particles generated from wear of spring in DC wall bushing were selected, the surface potential decay and the DC flashover voltage of epoxy attached with particles were measured. The results show that the discrete particles could increase surface trap level by 0.025 eV under the effect of Van der Waals force. Furthermore, the deeper traps could capture the charge during the streamer development and inhibit the flashover, when the particle amount less than 500 per mm2. If the particles are more enough to form the continuous paths, these conductive paths could promote the streamer to propagate, which shortens the insulation distance, increases the electric field, and decreases the flashover voltage by 50% finally.
