Negative Corona Research Articles

Trichel pulse characteristics and mechanism of negative corona discharge in sub-millimeter gaps

A negative corona discharge system of a needle-plate electrode suitable for sub-millimeter gaps is established to investigate Trichel pulse characteristics of negative corona discharge, in which an optical acquisition system is especially applied to timely observe a discharging corona. Electrostatics–hydrodynamics coupling simulations of air discharging in 100 μm-gaped needle-plate electrodes are performed to elucidate the micro-physical process of negative corona discharge. The impact ionization coefficient used for simulations and the experimentally recorded images of discharge corona are combined to characterize the active region of secondary electron emission. Dynamical distribution and transport of the charged particles are analyzed from multiphysics simulations to explain the microscopic mechanism for various stages of Trichel pulses. Even though the corona front near the plate electrode maintains a high rate of collision ionization and secondary electron excitation, the needle tip corona has not reached the threshold electric field of electron avalanche required for glow discharge, as manifested by discharge sawtooth waves comprised of corona and glow components. The amplitude and frequency of Trichel pulses increase, respectively, with impact ionization and secondary electron emission, which is evidently dependent on attachment coefficient and anion mobility. A higher attachment coefficient will lead to a significant reduction in amplitude of Trichel pulses. The present study provides a theoretical basis and experimental verification for micrometer discharges, which is the key point of insulation protections in microelectromechanical systems.

Negative DC corona patterns for different wire particle geometries in air insulation

This work deals with an investigation of negative corona discharge generated from standing wire particles in air insulation. Eight samples from different particle lengths and diameters were studied to understand the effect of particle geometries on discharge characteristics. The particle was stood artificially on the ground inside parallel plane electrodes and was energized with a positive HVDC generator. Pulse sequence analysis (PSA) technique was used to evaluate the corona discharge patterns and behaviors. Under the same applied voltage, it is concluded that an increase in particle length causes a rising trend on the average discharge current and pulse magnitude, as well as the pulses appear more frequent and fluctuate. Meanwhile, variation of the particle diameter shows that a larger particle size generates fewer pulses and a lower average discharge current. However, the pulse magnitude is higher and appears randomly with larger particle diameter. A simulation model based on Finite Element Method (FEM) was also established to explain the behaviors better. It is found that the pulse repetition rate is related to the electric field distribution and negative ions movement, while the pulse magnitude is related to ionization rate and positive ions velocity.

Dynamic interactive characteristics between icicle growth and corona discharge on HVDC outdoor insulators during icing accretion

AbstractIn order to improve the stability and reliability of high voltage direct current (HVDC) transmission lines in cold regions, this article investigated the corona discharges and the icicle growth characteristics on outdoor insulators under DC voltages. The experiments were conducted at CIGELE laboratory at University of Quebec. The simulation model of corona discharges and the theoretical model of icicle growth were established. The dynamic process and interactive characteristics between the icicle growth and corona discharges under different HVDC voltages were obtained. The results showed that the discharge activity was strong and the cooling effect of ionic air was weak under negative DC voltage, resulting in a large number of bubbles inside the icicle. More negative ions were produced under negative DC voltage, which enhanced the polarisation of water droplets, leading to a greater density of ice beads outside the icicles. In addition, the longest icicles of each insulator under high humidity could bridge the shed gap. The accumulated charge and leakage current were higher under negative DC voltage, as well as the corona discharge at the top of the icicles lasted longer. Therefore, the negative DC corona discharge more significantly inhibited the growth of the icicle, resulting in a slower growth rate of the icicles.

Children’s Symptoms with a Febrile Illness and a Positive or Negative Test of SARS-CoV-2 during the Omicron Wave

Febrile infections are common in childhood. Children can be infected with SARS-CoV-2, but their course is milder than in adults. So far, a comparison between febrile infections with a positive or negative Corona test with the Omicron variant is missing. The data used are from the FeverApp registry, which collects parent-reported data on febrile infections in children and informs about fever management. A comparison of symptomatic differences between episodes with a positive or negative Corona test was performed using Χ2-tests. During the Omicron wave, reported tests doubled and positive test results nearly 12-folded. In episodes with positive Corona saliva tests, more cough, fatigue, disturbed smell/taste, limb pain, sore throat, signs of serious sickness, and touch sensitivity were reported. Children with a negative Corona test show more tonsillitis, teething, any pain symptoms, earaches, and rashes. Thus, there are some significant differences between febrile infections with a positive or negative Corona test, but symptoms are present on both sides. The omicron variant seems to be more infectious than the alpha or delta variants in children, but the symptoms remain mild and do not differ much from other febrile infections.

Evolution of Negative Corona in the Discharge-Current Limitation Mode: Transition from the Pulsed-Periodic Mode to Steady-State Burning

The evolution of burning modes of a weak-current corona discharge in a diode filled with atmospheric air, having a pointed cathode and a flat anode, has been investigated. A theoretical description is performed in terms of an axisymmetric multifluid plasma model, including the kinetics of 9 types of particles and 25 plasma-chemical reactions. A discharge in a gap 10 mm long, with a needle-like cathode having a tip curvature radius of 100 μm, a source voltage of 8 kV, a ballast capacitance of 100 pF and a circuit ballast resistance of 1 MΩ, is described in detail. It is shown, both experimentally and theoretically, that the discharge has a lifetime of 180 μs and occurs in four clearly different stages under these conditions: (1) dark breakdown delay phase (0–20 μs); (2) Trichel pulse phase with a variable on–off time ratio and quasi-steady-state corona current component (20–80 μs); and (3) intermediate phase of monotonically rising weak current (80–130 μs), which ends with a vibrational transition to the (4) steady-state phase (130–180 μs), having a typical structure of glow discharge. The tendencies to a change in the corona discharge parameters with a variation in the feed voltage are analyzed. The results of theoretical calculations are in good agreement with the experimental data.

Comparison of Initiation and Temporal Evolution of Positive and Negative Ionic Wind Under Needle-to-Plate Electrode

Considerable research efforts have been devoted to the generation, characterization, and optimization of ionic wind produced by corona discharge. The current article tries to explain the mechanism that causes the different behaviors observed in negative and positive dc corona ionic wind. The steady-state and the transient state ionic wind produced by both polarities are studied through particle image velocimetry (PIV) technology. The results show that at transient state, a series of mushroom-like jets are produced in negative corona discharge ionic wind due to the effect of Trichel pulse. These jets merge with each other and combine momentum to form the wide structure at steady state. In comparison, the positive corona discharge current has no pulse, and the ionic wind has only one “I-shape” wave head during the initiation process. The dynamics of the jets is studied in detail. The formation of the jet series in negative corona, or single jet in the case of positive corona, is believed to play a key role in the generation of ionic wind.

Surface electric charge decay behavior of Polypropylene (PP) films treated by atmospheric air dielectric barrier discharge

Atmospheric air dielectric barrier discharge (DBD) is one of the most effective physical techniques for the cold plasma source. It is a promising technique used to modify the surface properties of polymers. This modification leads to improving wetting and adhesion properties, a change in surface roughness and other significant technological features. In recent studies, researchers have showed that DBD plasma exposure can modify the electric properties of insulating materials. In this study, we focused our attention on the influence of DBD plasma treatment on the surface electric charge behavior in polypropylene (PP) thin films. The effect of DBD plasma has been studied as a function of treatment time for two values of applied discharge voltages; 7 and 12 kV. After being exposed to DBD plasma, the samples were charged for 5 seconds in ambient air using a negative triode corona electrode system. The influence of DBD plasma treatment on the surface electric charge behaviour in PP thin films was investigated. The surface characterization of the untreated and treated PP films is performed using surface electric charge decay measurements, for identical charging conditions.

Experimental and Theoretical Study of Corona Inception Threshold in Rod to Plane Electrodes Under AC/DC Combined Voltage: Phase Corresponding to AC Voltage

Under AC/DC combined voltage, the corona inception phase corresponding to AC voltage is not a fixed value and will change within a certain range. In this article, the effects of DC polarity, DC proportion, rod radius, and rod-plane distance on corona inception phase were explored. The results showed that the normalized amplitude under equivalent positive corona conformed to normal distribution. In addition, with the increase of DC proportion, the distribution of corona inception phase under equivalent positive corona was more dispersed, and the dispersion changed more obviously than that under equivalent negative corona. When the DC proportion was increased from 25% to 75%, the interval width of phase under equivalent positive corona and equivalent negative corona increased by at most 50° and 15°, respectively. A fluid model was built to explain the change of phase dispersion from the perspective of space charge. The existence of corona inception phase resulted in the difference between AC instantaneous voltage and AC peak voltage at corona inception time, which was of great significance to the study of corona inception.

Evolution of Negative Corona in the Discharge-Current Limitation Mode: Transition from the Pulsed-Periodic Mode to Steady-State Burning

Evolution of Negative Corona in the Discharge-Current Limitation Mode: Transition from the Pulsed-Periodic Mode to Steady-State Burning

The current pulses characteristics of the negative corona discharge in SF6/CF4 mixtures

This paper presents the results of numerical investigation of the current pulses characteristics in SF6/CF4 mixtures for the negative point-plane corona discharge. The pressure and the temperature of gas mixtures are 0.4 MPa and 300 K, respectively. The CF4 content varies from 20% to 80%. The 2D axisymmetric geometry with point-plane electrodes is investigated, and the three drift-diffusion equations are solved to predict the characteristics of the negative corona discharge. In addition, Poisson’s equation is coupled with the above three continuity equations to calculate the electric field. In order to calculate the electron impact coefficients, including the Townsend ionization and attachment coefficients, as well as the mobilities and diffusion coefficients for electrons, the two-term Boltzmann equation is solved. The characteristics of three ionic species at five stages of the first current pulse in 60%SF6-40%CF4 and 20%SF6-80%CF4 mixtures are selected to discuss the development mechanism of current pulses. Moreover, the reduced electric field strengths at the corresponding time instants are presented to help understand the discharge process. The current waveform and the total number of three species are compared in all the cases to analyze the effects of the CF4 content on the discharge. The reduced electric field strength is also helpful in understanding the effects of CF4 content. When the CF4 content increases to 80%, the discharge is more intensive and the pulse frequency also increases.

Effect of Temperature on Current Pulse Characteristics of Negative Corona Discharge Based on Numerical Model

Temperature is an important factor affecting the dynamic processes of corona discharge, since the ionization, attachment, and mobility of charged particles are directly related to temperature. Most existing research has investigated the temperature effect on corona discharge through experimental works. However, they are hard to acquire the corona discharge microphysical processes, which are related to the formation of the current pulse and electromagnetic (EM) wave signals. This article proposes a numerical model with temperature-related transport parameters to study the temperature influence on microphysical processes and current pulses for negative corona. By comparing microphysical quantities such as the effective ionization coefficient, density, and velocity of space charges, the effect of temperature on the current pulse parameters including the rise and fall times, amplitude, and pulsewidth is systematically explained. It shows that as the temperature rises, the current pulse amplitude increases, while the other three parameters decrease. The rise time is dependent on the effective ionization coefficient. The fall time is affected by the velocities of negative and positive ions. The experimental results indicate the simulated current pulses are consistent with the measured ones, proving the effectiveness of the proposed numerical model with temperature variation.

IONIC WIND FLOW CHARACTERISTICS OF A MAGNETIC-FIELD-ENHANCED SOLID-STATE FAN AND ITS PERFORMANCE IN LIGHT-EMITTING DIODE COOLING APPLICATIONS

Solid-state fans (SSFs) have distinct advantages over traditional cooling fans in the thermal management of high-power electronics. In this work, a magnetic-field-enhanced SSF is proposed, and the physical model of negative corona discharge superimposed by an electromagnetic field is established. A computational model is used to calculate and analyze the effect of the magnetic field on the ionic wind distribution. The magnetic flux density and permanent magnet position distribution in the SSF are optimized experimentally, and the optimized SSF is applied to LED chip cooling. The findings show that adding a magnetic field encourages electrons to collide with neutral gas molecules and enhances the driving force of charged particles. The ionic wind velocity and mean driving force at the SSF's outlet will grow as magnetic flux density rises, and the ionic wind flow distribution will show apparent divergence. When the permanent magnet spacing is 15 mm, the highest ionic wind velocity is 2.82 m/s, and the mean driving force of SSF increases by 30.2%. The magnetic-field-enhanced SSF has a better LED-chip cooling effect, the maximum junction temperature drop is 11.6°C, and the cooling efficiency is higher. This research introduces a novel way of improving the cooling of electronics.

Experimental Comparison for effect of Positive and Negative Corona Discharge Plasmas on the Properties of Distilled Water

في هذا البحث تمت دراسة مقارنة تجريبية لتصريف البلازما الإيجابي والسلبي لتفريغ الهالة على الماء المقطر في درجة حرارة الغرفة والضغط الجوي عند الجهد العالي (0-10 كيلو فولت). باستخدام نظام من قطبين ، الأول هو قضيب نصف قطره 1 مم والآخر منحني الشكل نصف قطره 1 سم. أظهرت النتيجة أنه باستخدام بلازما التفريغ الإيجابي للإكليل ، تنخفض قوة PH الهيدروجين وترتفع المياه الحمضية عند زيادة الجهد ووقت التفريغ المستمر (دقيقتان من العلاج). بالإضافة إلى ذلك ، عندما تزداد مدة التفريغ الإيجابي للإكليل (0-10 دقائق) بجهد ثابت عند 5 كيلو فولت ، يؤدي إلى نفس النتيجة أعلاه. عند استخدام تصريف الهالة السلبية مع الماء المقطر ، تزداد قيمة PH وتصبح المياه قاعدة. يزداد إجمالي المواد الصلبة الذائبة (TDS) والتوصيل الكهربائي (EC) للماء المقطر في كل من تصريفات البلازما (الهالة الموجبة والسالبة) عن طريق رفع الجهد المعالج والوقت الثابت أيضًا ، ويزداد وقت التفريغ عندما يظل الجهد ثابتًا

Microscopic analysis of Trichel's pulse characteristics and the effect of air pressure and temperature

The negative direct current corona discharge experiment under the needle-plate electrode is conducted, and the typical Trichel pulse waveform is obtained. Furthermore, to analyze the microscopic process of corona discharge, a plasma-fluid discharge simulation model, including air chemical reactions, is established, and a Trichel pulse waveform is obtained, which is consistent with the experimentally obtained waveform. Thus, the chemical reaction that plays a dominant role in the generation and disappearance of charged particles as well as the spatiotemporal distribution and quantitative variation of charged particles during the discharge process are clarified. On this basis, the variation of the microscopic and macroscopic parameters in the discharge process under different air pressure and temperature conditions is studied. The results show that microscopic parameters, such as charge density and electric field intensity, are negatively associated with air pressure and positively associated with temperature, while macroscopic parameters, such as Trichel pulse average current, average peak current, and discharge frequency, are positively associated with the microscopic parameters.

Flight Demonstration of Net Electric Charge Control of Aircraft Using Corona Discharge

This article reports on a flight experiment demonstrating the ability to control the net electrical charge of a small unmanned aircraft using ion emission from a corona discharge. The charging mechanism is based on the advection of ions produced by the corona discharge, leaving charge of the opposite polarity on the aircraft. An onboard high voltage power supply of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 15 kV was remotely operated to control the level of charging. The high voltage terminal of the power supply was connected to two thin corona wires placed above the aft surface of the wing in the spanwise direction, whereas the low voltage terminal was connected to the conductive airframe. Using this strategy, electric potentials of up to −30 and +23 kV relative to the environment were acquired by the aircraft, using positive and negative corona discharges, respectively. The study addresses the dependencies with power supply bias and wind speed. Possible applications of net charge control include risk reduction of aircraft-triggered lightning strikes, as explored by the authors in prior work, as well as a means of compensating for precipitation static and other sources of charging.

Ionic wind of a needle-to-plate dielectric barrier discharge

The present study aims at investigating the ionic wind produced by a dielectric barrier discharge ignited between a needle and a grounded plate electrode covered by a dielectric material. The needle is powered by a sine high voltage vAC(t) and the electrode gap is equal to 15 mm. Preliminary measurements of the discharge current highlighted that two different discharges take place during one voltage cycle. During the positive going-cycle, there is a positive corona discharge composed of streamers, their frequency (close to 5 kHz) and magnitude (a few mA) increasing with the magnitude of the applied voltage. During the negative-going cycle, a negative corona discharge occurs, its current highlighting the presence of Trichel pulses whose the frequency varies between 100 kHz and 500 kHz.Then we investigated the ionic wind produced by the DBD with the help of a 20 kHz PIV system (particle image velocimetry) in order to access to time-averaged and time-resolved data. First, we charaterized the effect of the magnitude of vAC(t) and its frequency value fAC on the time-averaged ionic wind. Secondly, we investigated the temporal behavior of the ionic wind as a funtion of the high voltage frequency. Two main behaviors have been highlighted. At low frequency (up to 200 Hz), the sine high voltage results in a pulsed ionic wind, with a velocity peak at each half cycle: there is a first flow acceleration due to the positive corona discharge and a second one during the negative corona, the velocity during the positive discharge being higher than the one measured during the negative discharge. At higher frequency (from 500 Hz up to 1000 Hz), the positive ionic wind takes over the negative one and the velocity peak due to the negative discharge is very weak. At 2000 Hz, there is only one single flow acceleration per voltage cycle, because the ionic wind produced by the positive corona discharge takes totally over the ionic wind produced by the negative corona because it is more intense and faster.

Mitigating reverse emission in electroaerodynamic thrusters

Electroaerodynamic (EAD) thrusters have the potential to become a quieter and solid-state alternative to propellers in unmanned aircraft. An EAD thruster produces ions from atmospheric air and accelerates them across an electric field between two electrodes: an emitter, where ions are produced; and a collector, where they are neutralized. As ions drift from the emitter to the collector, they collide with neutral air molecules and transfer momentum to them, resulting in an ionic wind and a thrust force. Reverse emission from the collector is a major non-ideal effect in EAD systems that can reduce the efficiency of EAD thrusters: it increases the power draw of the device and eventually leads to electrical breakdown and sparking. Here, we perform a parametric study with a wire-to-cylinder electrode geometry using positive and negative corona discharges as well as wire-to-wire dielectric barrier discharges as ion sources. We show that reverse ion emission is primarily caused by a gas discharge at the tips of the cylindrical collectors, which increases current without contributing to thrust and produces audible noise. We identify three ways to mitigate reverse emission: increasing the collector diameter, increasing the collector span with respect to the emitter span, and attaching hemispherical end caps to the collector. By mitigating reverse emission, we show that the power draw of an EAD thruster can be significantly reduced (by up to 64% in our particular configuration) while still delivering the same thrust.

Negative corona discharge and flow characteristics of a two-stage needle-to-ring configuration ionic wind pump for temperature and relative humidity

Ionic wind pumps have the advantages of a compact structure, no moving parts, and low power consumption. The effects of temperature and humidity on the current–voltage and flow characteristics of ionic wind pumps are still unclear. This study experimentally investigates the effects of temperature and humidity on the breakdown voltage, discharge current, and velocity of a two-stage needle-to-ring type ionic wind pump with a negative corona discharge. It is found that the coupling effects of temperature, humidity, and water vapor condensation determine the current–voltage and flow characteristics of ionic wind pumps. The temperature and vapor condensation effects can enhance the discharge current and outlet velocity and weaken the breakdown voltage. However, the humidity effect can weaken the discharge current and outlet velocity, and improve the breakdown voltage. Moreover, there exists a competition between humidity and vapor condensation effects on breakdown voltage, current, and velocity. The increase in temperature intensifies the humidity effect and weakens the condensation effect; thus, the temperature changes the contribution of humidity and condensation effects in the competition. A working spectrum of ionic wind is provided in the temperature and humidity coupling environment, including a vapor condensation-controlled zone, a sensitive humidity zone for breakdown voltage and velocity, and an insensitive humidity zone for breakdown voltage and velocity. The spectrum can provide theoretical guidance for designing ionic wind pumps at different temperatures and humidity.

Ionic Charge Emission Into Fog From a Remotely Piloted Aircraft

AbstractCharge influences the properties of liquid droplets, such as evaporation rates, hydrodynamic stability, and sticking probabilities. Modifying droplet charge therefore provides a possible method of influencing fogs or clouds. An instrumented, remotely piloted aircraft has been equipped with positive and negative corona emitters to cause droplet charging. With the aircraft circling at 20 m altitude, effects of ion release were compared in clear air and natural fog. In clear air, the surface atmospheric electrical field changed whenever the emitters were activated, but without significant differences in the short‐wave radiation as the aircraft passed over previously ionized air. In fog, radiation fluctuations showed a Gaussian distribution before either emitter operated or when both emitters were operating, but with different distributions during unipolar ion emission. Introducing unipolar ions led to a maximum change in fog reflectivity of ∼2%, about 25 s later.

Investigation of negative corona discharge Trichel pulses for a needle-plane geometry via two numerical 2D axisymmetric models

Trichel pulses for negative direct current corona discharge in a pin plate configuration under open dry air conditions are investigated using two numerical models. The first well known general model takes electrons and positive and negative ions into consideration. The second model, a more detailed one, takes electrons and other 16 nitrogen and oxygen species into consideration. Both models are able to capture the general evolution of the electrical discharge. However, the detailed model is able to also show the effect of behavior and contribution of specific species on the discharge. The results show that negative oxygen ions play a key role in the development of Trichel pulses. Furthermore, O2− and O3− ions develop in the interlayered spatial layers in the discharge gap, with the number of layers corresponding to the number of Trichel pulses. It is also shown that nitrogen ions are mostly generated in front of the negatively biased (−5.5 kV) pin.