Characteristics Of Trichel Pulses Research Articles

Impact of Cathode Geometry on Negative Corona Discharge and Trichel Pulse Characteristics: A Comparative Analysis of Hyperbolic, Elliptic, and Tangent-Circular Needle Shapes

Impact of Cathode Geometry on Negative Corona Discharge and Trichel Pulse Characteristics: A Comparative Analysis of Hyperbolic, Elliptic, and Tangent-Circular Needle Shapes

Conic Cross-Sectional Electrodes and Their Influence on Negative Corona Discharge and Trichel Pulse Characteristics

Conic Cross-Sectional Electrodes and Their Influence on Negative Corona Discharge and Trichel Pulse Characteristics

Numerical approaches in simulating Trichel pulse characteristics in point-plane configuration

In this work, a detailed comparison is made of a few different approaches to numerical modeling of non-equilibrium gas discharge plasmas in dry ambient air at atmospheric conditions, leading to Trichel pulse discharge. Simulation models are based on a two-dimensional axisymmetric finite element discretization of point-plane geometry. The negative corona discharge and the hydrodynamic approximation for generic ionic species (electrons, positive and negative ions) are used. The models account for the drift, diffusion, and reactions of the species. They comprise continuity equations coupled to Poisson’s equation for the electric field. Three different formulations were used to specify the ionic reaction rate coefficients. In the first one, the reaction coefficients are approximated by the analytical expressions as a function of the electric field intensity. Two others extract the reaction coefficients from the solution of the Boltzmann equation as a function of the reduced electric field or the electron energy. The effect of gas flow and heating on the pulse characteristics is also investigated. The accuracy of the models has been validated by comparing them with the experimental data.

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.

Effect of Magnetic Field on Corona Discharge Under Airflow

Corona discharge under airflow is extensively researched due to its wide applications in the fields of electrostatic precipitator, flow control, thermal management, and so on. The adjustment of discharge characteristics has been an important research topic in recent years. In this article, a magnetic field is applied as a method to adjust the characteristics of corona discharge under airflow. The experimental result illustrates that the intensity and direction of the magnetic field would influence the turning point of the discharge state under airflow, and the corresponding discharge image and Trichel pulse characteristics, such as amplitude and frequency, would also be changed. The physical mechanism for this phenomenon is analyzed by considering the magnetic force of the corona discharge. With increasing magnetic field intensity, the pressure in the discharge space would change and the airflow state and the discharge process, as the ionization process and the attachment process, would be influenced. The overall characteristics of discharge under airflow would be adjusted by the magnetic field. The results illustrated that the magnetic field is possibly utilized to improve the application of corona discharge under airflow.

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.

Numerical simulation of the Trichel pulse characteristics in SF6/N2 gas mixtures

The paper presents the results of a numerical simulation of the effects of N2 on the characteristics of Trichel pulses in SF6 at 0.4 MPa. The simulation was performed in a 2D axisymmetric geometry assuming a three species discharge model for the applied voltage on the discharge electrode to be −25 kV. Three drift-diffusion equations coupled with Poisson's equation are considered to determine the dynamic behavior of Trichel pulses and the temporal and spatial distributions of charged species. The reduced ionization coefficient, the reduced attachment coefficient, the electron mobility, and the electron diffusion coefficient of SF6/N2 mixtures are obtained by solving the two-term Boltzmann equations. The content of N2 varies from 20% to 80%. The distribution of three charged species and the reduced electric field at the discharge tip are presented at different instants of time to explain the formation mechanism of the Trichel pulses in SF6/N2 mixtures. The time-dependent current, the total number of electrons, the positive ions, and the negative ions as well as the reduced electric field at the discharge tip under different SF6/N2 mixtures are analyzed to investigate the sensitivities of these properties to the N2 content.

Comparison of Dust Particle Dynamics Under Different Electrode Shapes at the Early Stage of Negative Corona Discharge

Electrode shape plays an important role in collecting efficiency of the arista electrode in electrostatic precipitation (ESP). Using hydrodynamic model coupled with Poisson’s equation and applying finite element method, the characteristics of Trichel pulse under hyperboloid electrode and hemispherical electrode were compared. The numerical model is established in dry air at atmospheric pressure, using a traditional needle-to-plane configuration, which is simplified from the model of arista electrode and a plate in ESP. Combined with the motion equation of dust particle, the motion characteristics of the dust particles at different positions in negative corona discharge with different electrode shapes are studied. Under the same average power, the anode of the hemispherical electrode collects more than twice as many dust particles as the hyperboloid electrode, and the number of dust particles attached to the cathode is a little less than that of the hyperboloid electrode, in the early stage of ESP.

An electric field measurement method based on electro-optical modulation for corona discharge in air.

To study corona discharge in air, it is important to measure the electric field in the discharge space, which is directly related to the corona discharge process. In this paper, we present a method for measuring the electric field with electro-optical modulation. This method uses space laser modulation based on Bi4Ge3O12 (BGO) crystals, and we suggest using the dual optical path difference method to improve the measurement performance. The measurement error is analyzed from theory, including the measurement error of a highly inhomogeneous electric field and the error due to theoretical approximation. In system calibration, the system noise and the dual optical path difference method were analyzed. The dynamic linear range is determined, and measurement effectiveness in the severely nonuniform electric field is verified by comparison with a finite element numerical simulation. We measured the electric field in Trichel pulses under negative dc voltage and found electric field pulses. These measurement results show that the characteristics of Trichel pulses are directly related to the electric field. Therefore, this method can provide strong support for the study of corona discharges.

The Effect of Environmental Temperature on Negative Corona Discharge Under the Action of Photoionization

The properties of corona discharge in practical applications are strongly influenced by the variation of environmental parameters. A 2-D axisymmetric hydrodynamic drift-diffusion model coupled with Poisson's equation and three Helmholtz differential equations is established to investigate the effect of environmental temperature on negative corona discharge under the action of photoionization. This numerical model is performed by a traditional needle-to-plane configuration in dry air at atmospheric pressure. The characteristics of Trichel pulses, negative ion density, electric field, and electron density are discussed in this paper. It is found that the magnitude of Trichel pulses, first pulse duration, and pulse frequency increase with increasing the ambient temperature. Moreover, the effect of photoionization under these conditions is also investigated by simulations intensively.

Characteristics of Trichel Pulse Parameters in Negative Corona Discharge

In order to investigate the characteristics of Trichel pulse in negative corona discharge, a corona discharge measurement system, and a simulation model are proposed. Pulse parameters fit by double exponential function are discussed in this paper. Effects of the magnitude, interval, crest time, and fall time of the pulse on the parameters are discussed for different applied voltages and radii of curvature of the needle electrode. Fitting functions under different conditions are also given in this paper.

Numerical study of the effect of the needle tip radius on the characteristics of Trichel pulses in negative corona discharges

This paper presents a numerical study of the impact of the needle tip radius on the electrical characteristics of Trichel pulses in negative corona discharges for a needle-plane configuration in atmospheric air. The radius of curvature of the needle tip varies from 20 μm to 45 μm. The first current pulse, subsequent pulse train is discussed here based on the distributions of charged species and electric field. Three species continuity equations along with Poisson's equation are solved by the hydrodynamic drift-diffusion approach, in which the role of photoionization is considered. The increasing needle tip radius reduces the peak of the first pulse significantly and delays the start of the first pulse, but almost keeps the duration of the first pulse constant. At the instant of the first pulse peak, both the magnitude of the charged species densities and the electric field decrease with the needle tip radius, and the electric field is strongly distorted by the space charge field. For the subsequent current pulses, the current magnitude is weakly related to the needle tip radius, whereas the pulse period is proportional to the needle tip radius. The increasing needle tip radius reduces the positive ion and electron densities but increases the negative ion density at the instant of the current pulse peak, which diminishes the difference of the electric field for different needle tip radii.

Experimental study of the characteristics of Trichel pulses in the needle-plane negative corona discharge in atmospheric air

The results of an experimental study of the negative corona discharge in a needle-plane geometry are reported in this paper. The experiments were conducted in air at room temperature and atmospheric pressure. The impact of different parameters: the needle voltage, needle-plane distance, and the radius of curvature of the needle's tip on the frequency, DC current and the temporal characteristics of the pulses (rise time, fall time and the pulse width) was studied. Four different needles with radii of curvatures ranging from 19 μm to 55 μm were used. The needle-plane distance was varied from 6 mm to 3 cm. The applied voltage on the needle was varied from the onset voltage (−4 kV to −6 kV) to −10 kV. It was observed that the temporal characteristics of the pulses, such as rise time, were not a function of the radius of the curvature of the needle's tip, voltage level, or the needle-plane distance. The experimental data were compared with the results of numerical simulations, as well as with the experimental data published by Lama and Gallo. The experimental findings were found to be in a good agreement with Lama's and Gallo's work. Some discrepancies were found between the numerical and experimental results, and possible reasons for those are discussed.

Parametric study of the characteristics of Trichel pulses in the needle-plane negative corona discharge in atmospheric air

A numerical study of the impact of different model coefficients on the frequency, DC current, and the rise time of the Trichel pulses in a needle-plane negative corona discharge is presented here. The studied coefficients include the coefficients of the ionization and attachment reactions, the mobilities of the three charged species considered in the model (electrons and positive and negative ions), and the coefficient of the secondary emission of electrons. The characteristics of the pulses were also studied using another set of model coefficients which includes an extended number of reactions such as detachment of the electrons from negative ions.

Trichel Pulse in Negative DC Corona discharge and Its Electromagnetic Radiations

We investigate in this paper the radiated electromagnetic waves together with the discharge characteristics of Trichel pulse of negative DC corona discharge in air in pin-to-plate and wire-to-plate configurations. The feature of the current pulse and the frequency spectrum of the electromagnetic radiations were measured under various pressures and gas gaps. The results show that the repetition frequency and the amplitude of Trichel pulse current depend on the discharge conditions, but the rising time of the pulse relates only to the radius of needle or wire and keeps constant even if the other conditions (including the discharge current, the gas gap and the gas pressure) change. There exists the characterized spectrum of electromagnetic waves from negative corona discharge in Trichel pulse regime. These characterized radiations do not change their frequency at a given cathode geometry even if the averaged current, the gas gap or the air pressure changes, but the amplitude of radiations changes accordingly. The characterized electromagnetic radiations from Trichel pulse corona relate to the formation or the rising edge of current pulse. It confirms that the characterized radiations from Trichel pulse supply information of discharge system and provide a potential method for detecting charged targets.

Spatio-temporal characteristics of Trichel pulse at low pressure

Trichel pulses are investigated using a needle-to-plane electrode geometry at low pressure. The evolution of current and voltage, the spatio-temporal discharge images of Trichel pulse are measured. The rising time and duration time in a pulse are about 10 μs and several tens of microseconds, respectively. One period of pulse can be divided into three stages: the stage preceding cathode breakdown, cathode glow formation, and discharge decaying process. Besides a cathode glow and a dark space, an anode glow is also observed. The emission spectra mainly originate from the C3Пu → B3Пg transition for nitrogen. In addition, the capacitances in parallel connected with the discharge cell have important influence on the pulsing frequency.

Influence of gap spacing on the characteristics of Trichel pulse generated in point-to-plane discharge gaps

In this paper, the specific characteristics of the Trichel pulse generated in wide point-to-plane discharge gaps are investigated and compared with those of the currents generated in narrow gaps. A set of empirical formulas are derived to describe the specific characteristics. The influence of the gap spacing both on the current characteristics and on the coefficients of the formulas is studied. Based on the experiment results, an improvement is made to the space charge calculation method proposed by Lama and Gallo [J. Appl. Phys. 45, 103–113 (1974)] and the calculation results are compared to the ones obtained with Lama and Gallo's original method. With the influence of the space charge considered, the modified method obtains more accurate results of the space charge accumulating in the gap and gives a more precise description of the motion of the space charge in the gap. Based on the calculation results, the influence of the space charge on the distribution of the electric field is examined and the influence of the gap spacing on the current characteristics is also studied.

Specific characteristics of negative corona currents generated in short point-plane gap

The Trichel pulse is a typical kind of negative corona current observed in electronegative gases with a highly regular form. The characteristics of the Trichel pulse, such as the repetition frequency, the amplitude of each pulse, and the mean current, are dependent on different discharge conditions. Quite many scholars have studied the mean current and the current-voltage characteristic of Trichel pulses, yet the specific characteristics of the pulses have barely been investigated. In this paper, a series of experiments were carried out in a short point-to-plane discharge gap to investigate the detailed characteristics of Trichel pulses. After numerical fitting of the experiment results was performed, a new set of empirical formulas were derived to predict the specific characteristics of the negative corona current under different conditions. Different from existing literature, this paper uses as variables the average electric field intensity and the corona inception field intensity which is independent of the gap spacing in the empirical formulas. In the experiments, an inverse correlation between amplitude and repetition frequency of the pulses was observed. Based on the investigation of the remaining space charge in the discharge gap, this correlation is theoretically proved to be caused by the influence of space charges.

Trichel pulses in a negative corona discharge in air at low pressure

Most works focused on the Trichel pulses at an atmosphere pressure in the past. In this paper, the characteristics of Trichel pulses at low pressure (several Torr) in air used by a needle-to-plane discharge structure are investigated. The current-voltage (I-V) characteristics, the images of discharge and the time evolution of the current and voltage of Trichel pulses are measured under different conditions. Results show that Trichel pulses exist in the negative differential resistance of I-V curves, and disappear when the discharge transits to the abnormal glow discharge mode with an abrupt contraction of discharge area around the needle tip. The pulses are consisted of a very short rising time (about 10 μs) and a short durations time (tens of μs) separated by longer inter-pulse periods (more than 100 μs). The frequency of pulses can be tuned continuously from a few kilohertz to more than ten kilohertz by adjusting the averaged current and the pressure. It increases with the increase of averaged current at the same pressure, and rises as the pressure increasing at the same averaged current. These results will be helpful to understand the mechanism of Trichel pulses.

A numerical model of Trichel pulses in air; the effect of pressure

In this paper a three-species two-dimensional numerical model is used for the simulation of the Trichel pulse regime of corona discharge in air in a point-plane configuration. The effect of air pressure on Trichel pulse characteristics is investigated and the numerical results are compared with the available experimental data. The effect of corona electrode radius of curvature on charge per pulse and the relation between charge per pulse and the average charge per pulse is also studied, and compared with the experimental data reported by Atten et al.