Streamer Corona Research Articles

Influence of voltage magnitude on the dynamic behavior of a stable helium atmospheric pressure plasma jet

Effects of voltage magnitude on the development of a stable helium atmospheric pressure plasma jet are investigated by current measurements and high temporal-resolution streak images. Generated by a coaxial dielectric barrier discharge structure, the entire discharge can be classified into three regions: discharges in the tube gap, downstream jet, and up-streamer. The discharge morphologies of each region are analyzed. In the positive discharge phase, there are two discharges in the tube gap between the electrodes; the first one is ignited as corona and then developed into streamer corona, and the second one is similar with positive glow. The downstream jet is ignited independently from the discharge in the tube gap. Referred as “plasma bullet,” the dynamic behavior of the jet can be well described as a positive streamer. Under specific applied voltage, the jet is found to be composed by double bullets in which case the jet length decreases since that less charge is carried by the first bullet. The up-streamer can be captured as long as the discharge in the tube gap is activated. Propagating with velocity of ∼4 km/s, the up-streamer can be regarded as the extension of the first discharge in the tube gap. In the negative discharge phase, the discharge is confined in the tube gap with nearly symmetrical morphology with the positive one. Besides, with the rising of voltage, the negative discharge is initially intensified and then turns weaker after surpassing certain voltage, which may provide suitable condition for the occurrence of double-bullet phenomenon.

코로나 방전 플라즈마를 이용한 화산암재 분말 살균

Atmospheric-pressure nonthermal corona discharge plasma was applied to the sterilization of biologically contaminated scoria powder. Escherichia coli (E. coli) culture solution was uniformly sprayed throughout the scoria powder for artificial in- oculation, which was well mixed to ensure uniformity of the batch. The effect of the key parameters such as discharge power, treatment time, type of gas and electrode distance on the sterilization efficiency was examined and discussed. The experimental results revealed that the plasma treatment was very effective for the sterilization of scoria powder; 5-min treatment at 15 W could sterilize more than 99.9% of E. coli inoculated into the scoria powder. Increasing the discharge power, treatment time or applied voltage led to an improvement in the sterilization efficiency. The effect of type of gas on the sterilization efficiency was in order of oxygen, synthetic air (20% oxygen) and nitrogen from high to low. The inactivation of E. coli under the influence of corona discharge plasma can be explained by cell membrane erosion or etching resulting from UV and reactive oxidizing species (oxygen radical, OH radical, ozone, etc.), and the destruction of E. coli cell membrane by the physical action of numerous corona streamers.

Fast imaging of intermittent electrospraying of water with positive corona discharge

The effect of the electrospraying of water in combination with a positive direct current (dc) streamer corona discharge generated in air was investigated in this paper. We employed high-speed camera visualizations and oscilloscopic discharge current measurements in combination with an intensified charge-coupled device camera for fast time-resolved imaging. The repetitive process of Taylor cone formation and droplet formation from the mass fragments of water during the electrospray was visualized. Depending on the applied voltage, the following intermittent modes of electrospraying typical for water were observed: dripping mode, spindle mode, and oscillating-spindle mode. The observed electrospraying modes were repetitive with a frequency of a few hundreds of Hz, as measured from the fast image sequences. This frequency agreed well with the frequency of the measured streamer current pulses. The presence of filamentary streamer discharges at relatively low voltages probably prevented the establishment of a continuous electrospray in the cone–jet mode. After each streamer, a positive glow corona discharge was established on the water filament tip, and it propagated from the stressed electrode along with the water filament elongation. The results show a reciprocal character of intermittent electrospraying of water, and the presence of corona discharge, where both the electrospray and the discharge affect each other. The generation of a corona discharge from the water cone depended on the repetitive process of the cone formation. Also, the propagation and curvature of the water filament were influenced by the discharge and its resultant space charge. Furthermore, these phenomena were partially influenced by the water conductivity.

Streptococci biofilm decontamination on teeth by low-temperature air plasma of dc corona discharges

Non-thermal plasmas of atmospheric pressure air direct current corona discharges were investigated for potential applications in dental medicine. The objective of this ex vivo study was to apply cold plasmas for the decontamination of Streptococci biofilm grown on extracted human teeth, and to estimate their antimicrobial efficiency and the plasma's impact on the enamel and dentine of the treated tooth surfaces. The results show that both positive streamer and negative Trichel pulse coronas can reduce bacterial population in the biofilm by up to 3 logs in a 10 min exposure time. This bactericidal effect can be reached faster (within 5 min) by electrostatic spraying of water through the discharge onto the treated tooth surface. Examination of the tooth surface after plasma exposure by infrared spectroscopy and scanning electron microscopy did not show any significant alteration in the tooth material composition or the tooth surface structures.

On a criterion of the appearance of an upward leader from ground-based objects

Results of an experimental study of processes forming an upward leader discharge from a grounded rod electrode in the electric field of an artificial cloud of charged water aerosol are presented. The transition of the streamer corona flash to an upward leader discharge was found to be of a probabilistic character and to be determined, first of all, not by the current amplitude, and not only by the flash charge passing through the stem of the pulse corona, but by a set of parameters: duration of the current passage at a rather high level and optimum value of the corona charge passed through the stem base. The range of radii of curvature of the rod-shaped lightning arrester tip (from 20 to 25 mm) at which the highest probability of the appearance of an upward leader is observed has been revealed.

FDTD Simulations of Corona Effect on Lightning-Induced Voltages

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to analysis of lightning-induced voltages at different points along a 5-mm radius, 1-km long single overhead wire taking into account corona space charge around the wire. Both perfectly conducting and lossy ground cases were considered. FDTD computations were performed using a 3-D nonuniform grid. The progression of corona streamers from the wire is represented as the radial expansion of cylindrical weakly conducting (40 μS/m) region around the wire. The magnitudes of FDTD-computed lightning-induced voltages in the presence of corona discharge are larger than those computed without considering corona. The observed trend is in agreement with that reported by Nucci et al. and by Dragan et al ., although the increase predicted by our full-wave model (up to 5% and 9% for negative and positive lightning return strokes, respectively) is less significant than in their studies (up to a factor of 2) based on the distributed-circuit model with sources specified using the electromagnetic field theory. The disparity is likely to be related to the use of different charge-voltage diagrams, explicitly assumed by Nucci et al. and Dragan et al . and resulting from our FDTD model with corona in the present study. When corona is considered, there is a tendency for induced-voltage rise time to increase. It appears that the distributed impedance discontinuity, associated with the corona development on the wire, is the primary reason for higher induced-voltage peaks and longer voltage rise times, compared to the case without corona.

High‐speed video observations of a natural negative stepped leader and subsequent dart‐stepped leader

AbstractWe present new high‐speed video observations of a natural negative stepped leader and a subsequent negative dart‐stepped leader. Observations were made at a distance of 770 m using a high‐speed video camera at 10,000 frames per second, a microwave‐frequency radio receiver, a broadband electric field antenna, and an avalanche photodiode array. Lightning leader breakdown was observed in detail for both the negative stepped leader and the subsequent dart‐stepped leader. During the negative stepped leader breakdown, detailed images were captured of the discharge structures near the leader tips. These structures bear a remarkable resemblance to the corona streamer zone and space leader discharges that have been observed in laboratory‐generated negative stepped leaders. During the dart‐stepped leader breakdown, no corona streamer zone was observed outside of the decaying return stroke channel, but small luminous structures that are suggestive of space leaders were observed just ahead of the main dart leader tip. Two distinct low‐luminosity zones were observed just ahead of the dart leader tip, suggestive of two distinct breakdown regimes. A multipath junction was observed in the main channel to ground following the first return stroke but was not observed following the second return stroke. Finally, microwave‐frequency radio emissions for both leader types and their return strokes were recorded, and their time domain behavior is compared and discussed.

Aerosol formation from styrene removal with an AC/DC streamer corona plasma system in air

This paper reports aerosol formation from styrene removal with an AC/DC streamer corona plasma system in air. Aerosol formation from ozone-induced styrene removal is also investigated to further understand the aerosol formation process, and aerosol number concentration and size distribution inside the plasma system. For ozone-induced styrene removal, aerosols show a bi-modal-like size distribution. However, for non-thermal plasma induced styrene removal, aerosols show a mono-modal-like size distribution due to electrostatic force between charged aerosols. The total number concentration of these non-thermal plasma aerosols is around 1×106cm−3 with diameters between 28 and 157nm. The non-thermal plasma induced both polymerization and oxidation processes contribute to the aerosol formation. Aerosol carbons are about 61% of CC and/or CH, 22% of COC and/or COH, 15% of CO, HCO and/or aromatic-OH, and 2% of COOH and/or COOR related compounds. The non-thermal plasma can be used not only for styrene removal, but also for by-product aerosol collection.

FDTD Simulation of Insulator Voltages at a Lightning-Struck Tower Considering Ground-Wire Corona

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to the analysis of transient voltages across insulators of a transmission line struck by lightning. In the simulation, three 60-m towers, separated by 200 m, with one overhead ground wire and three-phase conductors are employed. The progression of corona streamers from the ground wire is represented as the radial expansion of cylindrical conducting region around the wire. On the basis of the computed results, the effect of corona discharge at the ground wire on transient insulator voltages is examined. The insulator voltages are reduced by corona discharge on the ground wire. The reduction of insulator-voltage peak due to the ground-wire corona is not very significant: the upper-, middle-, and lower-phase-voltage peaks are reduced by 15, 14, and 13% for a positive stroke with 50-kA-peak and 3-μs-risetime current, and those for the negative stroke with the same current waveform parameters are reduced by 10, 9, and 8%, respectively.

Generation of non-thermal plasma combined with catalysts and their application in environmental technology

Non-thermal plasma (NTP) promotes formation and reaction of radicals at low temperature condition. In order to use NTP, selectivity and energy efficiency should be improved. For this purpose combination of NTP and catalysts has been proposed for several industrial applications. Several systems are at first introduced in this review, and then generation of NTP suitable for combination with catalysts will be introduced. The first generation of NTP combined with catalysts was a pulsed streamer corona with a TiO2 solid catalyst. This combination has been commercialized successfully as an indoor air cleaner attached to an air conditioner. However, this system cannot use honeycomb catalysts. A packed bed has therefore been used for testing the combination of NTP and pellet type catalysts. Packed bed uses a layer of ferroelectric pellets of a few mm in diameter. The pellet layer is sandwiched by the electrode energized with AC or pulsed voltages. Each contacting point of the pellets is ionized. The packed bed can be an important candidate for plasma-assisted combustion. An existing application for the packed bed is the volatile organic compounds (VOCs) decomposition. Recently, discharges in honeycomb catalysts have been developed. One end of a honeycomb catalyst is attached with a packed bed or a surface dielectric barrier discharge to generate NTP. This electrode serves as a plasma electrode. When a DC electric field is applied, ionization proceeds along the surface of fine channels of ceramic honeycomb. This honeycomb discharge could be used for various processes to combine NTP and catalysts. It could also be used for surface treatment of honeycomb catalysts by NTP.

Influence of the capillary on the ignition of the transient spark discharge

A self-pulsing negative dc discharge in argon generated in a needle-to-plane geometry at open atmosphere is investigated. Additionally, the needle electrode can be surrounded by a quartz capillary. It is shown that the relative position of the capillary end to the needle tip strongly influences the discharge inception and its spatio-temporal dynamics. Without the capillary for the selected working parameters a streamer corona is ignited, but when the capillary surrounds the needle, the transient spark (TS) discharge is ignited after a pre-streamer (PS) occurs. The time between PS and TS discharge depends on the relative capillary end position. The existence of the PS is confirmed by electro-optical characterization. Furthermore, spectrally and spatio-temporally resolved cross-correlation spectroscopy is applied to show the most active region of pre-phase emission activity as indicators for high local electric field strength. The results indicate that with a capillary in place, the necessary energy input of the pre-phase into the system is mainly reduced by additional electrical fields at the capillary edge. Even such a small change as a shift of dielectric surface close to the plasma largely changes the energy balance in the system.

Glow corona generation and streamer inception at the tip of grounded objects during thunderstorms: revisited

The initiation of streamers prior to a lightning strike can be reportedly inhibited by glow corona discharges generated from tall objects. In contrast to previous studies based on a simplified one-dimensional model of glow corona, a two-dimensional evaluation of the corona ion drift from tall objects is used here to analyse this effect quantitatively. Proper estimates for the corona space charge distribution generated during both the charging process of a thundercloud and the descent of the downward stepped leader are thus calculated. It is found that the shielding effect of the corona space charge on the streamer inception is not as severe as previously reported. Estimations of the effective height of the downward leader tip at which streamer inception takes place are presented and discussed for lightning rods and dissipation array systems.

Time-lag properties of corona streamer discharges between impulse sphere and dc needle electrodes under atmospheric air conditions

In this study of corona streamer discharges from an impulse generator using a dc power supply, the relationship of the discharge time-lag with the dc bias voltage between the sphere-to-needle electrodes under atmospheric conditions is investigated. Devices utilizing corona discharges have been used to purify air or water, destroy bacteria, and to remove undesirable substances, and in order to achieve fast response times and high power efficiencies in such devices, it is important to minimize the time-lag of the corona discharge. Our experimental results show that (a) the discharge path of a negatively biased needle electrode will be straighter than that of a positively biased needle and (b) the discharge threshold voltage in both the positive and the negative needle electrodes is nearly equal to 33 kV. By expressing the discharge voltage as a power function of time-lag, the extent of corona generation can be quantitatively specified using the exponent of this power function. The observed behavior of a corona streamer discharge between the negative spherical and the positive needle electrodes indicates that the largest power exponent is associated with the shortest time-lag, owing to the reduction in the statistical time-lag in the absence of a formative time-lag.

Streamer Corona Plasma Assisted Nonpremixed Flame Holding of a Propane Jet

A streamer corona discharge plasma was used to assist a propane-jet flame. The nonequilibrium plasma was produced by a 10k Hz sinusoidal power source. The experimental results shows that a streamer corona was generated between the flame edge and the nozzle, and the use of the streamer corona plasma discharge resulted in significant increase in flame stability.

Gas Heating and Formation of Single Liner Discharge Channel on Repetitive Branched Streamer Corona

Under non-uniform field in atmospheric short-gap, the branched pulse streamer corona changes to single liner discharge channel (SLDC) for a split second just before sparkover occurs. This SLDC is pre-transitional phenomenon of sparkover. Therefore, it is very important to study SLDC for understanding sparkover process. In this work, the SLDC was recreated well by applying highly repetitive impulse voltage to needle to plane gap in synthetic air with dilute CO2. The characteristics of SLDC including the channel temperature, the propagation of streamer head and the formation process were revealed by means of ICCD cameras and a spectroscopic measurement system.

Hydrophilic property of 316L stainless steel after treatment by atmospheric pressure corona streamer plasma using surface-sensitive analyses

Surgical-grade 316L stainless steel (SS 316L) had its surface hydrophilic property enhanced by processing in a corona streamer plasma reactor using O2 gas mixed with Ar at atmospheric pressure. Reactor excitation was 60Hz ac high-voltage (0–10kVRMS) applied to a multi-needle-to-grounded screen electrode configuration. The treated surface was characterized with a contact angle tester. Surface free energy (SFE) for the treated stainless steel increased measurably compared to the untreated surface. The Ar–O2 plasma was more effective in enhancing the SFE than Ar-only plasma. Optimum conditions for the plasma treatment system used in this study were obtained. X-ray photoelectron spectroscopy (XPS) characterization of the chemical composition of the treated surfaces confirms the existence of new oxygen-containing functional groups contributing to the change in the hydrophilic nature of the surface. These new functional groups were generated by surface reactions caused by reactive oxidation of substrate species. Atomic force microscopy (AFM) images were generated to investigate morphological and roughness changes on the plasma treated surfaces. The aging effect in air after treatment was also studied.

Simulation of leader speeds at gigantic jet altitudes

Lightning leaders advance in space by creating a heating conversion zone in their tips (i.e., streamer‐to‐leader transition) in which Joule heating produced by currents of many non‐thermal corona streamers transforms into a hot and conducting leader channel. It is believed that the initial stages of transient luminous events termed gigantic jets (GJs) propagating toward the lower ionosphere are directly related to leaders initiated by conventional intra‐cloud lightning discharges and escaping upward from thundercloud tops. In the present work we provide quantitative description of speeds of these leaders as a function of leader current and ambient air density (altitude). The direct comparisons with available experimental data indicate that the initial speeds of GJs of ∼50 km/s are consistent with leaders possessing currents 2–8 A. The observed acceleration of GJs can be explained by growth of the leader current, and at high altitudes (low air densities) may be significantly affected by predominance of non‐thermal (i.e., streamer) discharge forms.

A Simplified Model of Corona Discharge on Overhead Wire for FDTD Computations

A simplified model of corona discharge on overhead wire has been proposed for propagating surge computations using the finite-difference time-domain method. The radial progression of corona streamers from the wire is represented as the radial expansion of cylindrical conducting region whose conductivity is several tens of microsiemens per meter. Two wire radii are considered: 5 and 2 mm, in order to simulate two experimental con- figurations by Noda. The critical electric field on the surface of a 5-mm radius wire for corona initiation is set to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 1.8 or 2.9 MV/m. For a 2-mm radius wire, it is set to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 2.2 MV/m. The critical background electric field necessary for streamer propagation is set to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cp</sub> = 0.5 MV/m for positive voltage application, and E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cn</sub> = 1.5 MV/m for negative voltage application. The computed waveform of radial current (including both conduction and displacement currents) agrees well with the corresponding measured waveform. Also, the computed relation between the total charge (charge residing on the wire and emanated corona charge) and applied voltage (qV curve) agrees well with the corresponding measured one, except for relatively low applied voltages. Additionally, the increase of coupling between the energized wire and another one nearby due to corona discharge is well reproduced.

Corona Discharge With Electrospraying System for Phenol Removal From Water

In the present work, a pulsed pin-to-plate corona reactor has been used for phenol removal from water. The main advantage of the present reactor is the presence of electrospraying of water drops at the tip of the discharge pin simultaneously with corona streamer. Electrospraying increases the treated surface area and therefore increases the efficiency of the water treatment. Also, the microdroplets of the sprayed water pass through the different regions of the discharge streamer and hence are in contact with the different plasma species which enhances the treatment process. The physical and chemical reactions of the plasma species affecting the phenol treatment have been discussed. Effects of the applied voltage, the running number of re-treatments, the phenol concentration, and the type of the working gas on the treatment process have been studied. At optimum conditions of the reactor, a percentage removal of phenol of 99.5% has been achieved with an efficiency of 2.5 g/kWh.

Behaviors of Plasma Bullet Propagation and Effects of Gas Flow Rate

An Ar dielectric-barrier-discharge atmospheric-pressure plasma jet (APPJ) driven by a 34-kHz sinusoidal power source is employed to investigate plasma bullet propagation in positive and negative half cycles by using an intensified charge-coupled device camera. The effects of different Ar gas flow rates on plasma bullet behavior are also presented in this paper. It is found that the duration and velocity of bullets in a positive discharge current pulse are significantly shorter and faster than those in a negative discharge current pulse and APPJ seems easier to form the plasma bullet phenomena during the positive discharge current pulse. The differences between positive and negative discharge current pulses can be explained by using the cathode-directed streamer and negative corona theories, respectively. It is considered that, due to the possible turbulence flow, the propagation length of plasma bullets is decreased with the increment of gas flow rates.