Trichel Pulses Research Articles

Investigation of a single barrier discharge in submillimeter air gaps. Nonuniform field

Pulse characteristics of single barrier discharges as well as parameters of charges accumulated on the surface of a dielectric under the atmospheric pressure in the “needle-(0.1–2.0)-mm air gap-polymer barrier-plane” system are investigated. It is found experimentally that for the positive polarity of the needle, the voltage for the discharge initiation is higher than in the case of the negative polarity by ∼25–35%. The reversal of the needle polarity from negative to positive increases the amplitude of the discharge current and the accumulated surface charge by ∼1.5–3 times. For the positive polarity of the needle, the discharge is governed by a streamer mechanism, while for the negative polarity, the discharge is initiated by the formation of a single Trichel pulse. The single pulse regime is observed for the discharge current up to a certain electrode gap dCR. For the positive needle and for air gap width dair > dCR ≈ 1.5 mm, a multipulse burst corona is formed, while for the negative needle and dair > dCR ≈ 0.9 mm, a damped sequence of Trichel pulses evolves in the system.

Verification of positive streamer mechanism for negative corona Trichel pulses in O2/H2 mixtures

Abstract Current waveforms of the first negative corona pulses have been measured in O 2 + H 2 mixtures at a pressure range from 27 kPa to 50 kPa. It was observed that the hydrogen admixtures less than 4% do not change significantly the pulse current waveforms. Effects of changing cathode secondary electron emission were studied using a copper cathode coated by CuI and graphite. The results obtained support the theory of the cathode-directed streamer formation during the negative corona pulse rise.

Effect of humidity on negative corona Trichel pulses

The effects of environmental parameters, e.g., humidity, on the corona discharges in practical applications are important. A two-dimensional (2D) hydrodynamic drift-diffusion model has been used to investigate the effects of humidity on the negative corona Trichel pulses (TPs). The simulations are performed with a conventional needle-to-plate configuration in humid air. It is found that the magnitude of TPs grows gradually with increasing humidity and the frequency of TPs increases with humidity. The movements and formations of charged particles are faster in higher humidity. The numerical results are consistent with the experimental observation.

Respiratory Monitoring by a Field Ionization Sensor Based on Trichel Pulses

In this paper, a novel method for respiratory monitoring is presented. The method is based on Trichel pulses (TPs) using a simple field ionization sensor which consists of a needle electrode and a plate electrode. Experiments have been conducted to demonstrate that different respiratory patterns, including normal, ultra-fast, deep breaths, and apnea could be easily monitored in real time by detecting the changes in the TP frequency. The vital capacity could also be assessed by calculating the variation of TP frequency. It is found that the operation principle of the proposed sensor is based on the effects of breath airflow and the atomized water in exhaled air on the TP frequency by changing the ionization process and the dynamics of charged particles in the short gap. The influences of applied voltage and ambient parameters have also been investigated.

Polarity effect on the electrohydrodynamic (EHD) spray of water

This paper presents the effects of polarity on the electrohydrodynamic (EHD) spray of water (deionized and tap water) in air and pure CO2 environments. Its influence in the interaction of the EHD spray and corona discharges was experimentally measured and analyzed. In contrast to the various spray patterns observed under positive polarity, negative polarity induced only two modes (dripping and spindle) under the typical conditions used in this study. Mapping of electrospray modes is presented in conjunction with current–voltage characteristics, discharge and spray images obtained with ICCD and high-speed camera. We also first report the intermittent multi-jet mode in water in pure CO2. The essential differences in the spindle mode were the shape and elongation direction of the water filaments according to the negative or positive polarity. The different spray patterns in the spindle mode seemed to be associated with the movement of ion species in water. From the combined analysis of the corona discharges, one may conclude that the different properties of the coronas were associated with the spray patterns in both air and pure CO2. Typical onset streamers in air under positive polarity had minimal influence on the spray mode because they were found to be separated in time and space from the water meniscus. In contrast to the stable glow under positive polarity, many current pulses (Trichel pulse) were observed in the negative EHD spray.

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.

Modeling of Trichel Pulses in the Negative Corona on a Line-to-Plane Geometry

In this paper, a 2-D time domain method is proposed to simulate Trichel pulses in the negative corona discharge on a line-to-plane geometry. Three ionic species in the ionization layer, including electrons, positive ions, and negative ions, are taken into consideration. The FEM is used to solve the Poisson's equation, while the finite volume method is used to solve the charge transport equations. Trichel pulses on a line-to-plane geometry are analyzed and compared with the measured results of a designed experiment in the laboratory. Good agreement is obtained between the calculated results and the measured ones, verifying the validity of the proposed scheme.

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.

Numerical studies of Trichel pulses in airflows

In this paper the Trichel pulse regime of corona discharge in airflows is numerically studied with a two-dimensional model. The model is based on the hydrodynamic drift–diffusion approximation, taking into consideration the flow of the air in the discharge gap. Both transverse and longitudinal airflows under different conditions have been investigated. The influences of airflows on the characteristics of the Trichel pulses were clearly observed and analysed. The simulation results proved to be compatible with experimental analysis reported in the literature.

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.

On the Electrical Characteristic of Atmospheric Pressure Air/He/<formula formulatype="inline"><tex Notation="TeX">${\rm O}_{2}/{\rm N}_{2}$</tex></formula>/Ar Plasma Needle

The electrical characteristics of an air plasma needle are investigated. The discharge is driven by pulsed direct current voltages. A series of discharge pulses appear for one applied voltage pulse. The interval between nearby discharge current is tens of nanoseconds, which corresponds to a frequency of tens of MHz. This is much higher than that of the Trichel pulse (tens of kHz). The frequency of the discharge current pulses increases with the applied voltage but decreases with the gas gap distance. The series current pulses are found not only existing in electronegative gases (air, pure O2), but also in Ar and N2. On the other hand, when He is used, there always appears only one discharge current pulse; by adding small percentage of O2 to He, multiple discharges appear again.

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.

Nanoparticles formation and deposition in the trichel pulse corona

Cathode erosion in the negative corona discharge has been studied in the point-to-plane electrode configuration with Cu cathodes in the Trichel pulse regime. Redeposition of erosion products has been found on the cathode surface in form of agglomerates of 10-nm nanoparticles. Nanocraters and nanoparticles formation in the negative corona discharge has been considered in frames of electro-explosive mechanism of cathode erosion. According to this mechanism the cathode erosion is performed as a consequence of elementary erosion events each of which is caused by a Trichel pulse. A 1-dimentional model of corona-produced nanoparticles dynamics in the gap was elaborated. According to results of the simulation, the redeposition is explained by charging of the nanoparticles due to positive ions adsorption and thermionic emission. The size, temperature and initial velocity of the aerosol nanoparticles have the decisive action on redeposition in the negative corona discharge.

Investigation on Microcosmic Characteristics of Trichel Pulse in Bar-Plate DC Negative Corona Discharge Based on a Novel Simulation Model

An improved multi-component two-dimensional hybrid model is presented for the simulation of Trichel pulse corona discharge in dry air (O2:N2=1:4). The model is based on the plasma hydrodynamics and the chemical models, in which 12 species (e, O, O2, O3, O2+, O4+, O2-, O-, N2, N2+, N4+, and N2O2+) and 27 collision reactions between them are considered. In addition, the photoionization and secondary electron emission effect are also incorporated within the model as well. The simulation is established with a bar-plate electrode configuration with an inter-electrode gap of 3.3 mm where the negative DC voltage applied to the bar is 5.0 kV, the pressure in air discharge is fixed at 1.0 atm, and the gas temperature is assumed to be a constant (300 K). Based on the novel model, a few key microcosmic characteristics such as electric field distribution, net charge density distribution, electron density distribution at 5 typical time points during a process of Trichel pulse are discussed emphatically. What is more, the investigation on electron generation and disappearance rates, as well as positive ion, negative ion and neutral particle distribution characteristic along the axis of symmetry in the later Trichel pulse cycle are also detailed. The obtained results will provide valuable insights to the physical mechanism of negative corona discharge in air

Decontamination of Streptococci biofilms and Bacillus cereus spores on plastic surfaces with DC and pulsed corona discharges

Cold air plasmas of DC and pulsed corona discharges: positive streamers and negative Trichel pulses were used for bio-decontamination of Streptococci biofilm and Bacillus cereus spores on polypropylene plastic surfaces. The reduction of bacterial population (evaluated as log10) in the biofilm on plastic surfaces treated by DC corona reached 2.4 logs with 10 min treatment time and 3.3 logs with 2 min treatment time with water spraying. The enhancement of plasma biocidal effects on the biofilm by electro-spraying of water through a hollow needle high-voltage electrode was investigated. No significant polarity effect was found with DC corona. Pulsed corona was demonstrated slightly more bactericidal for spores, especially in the negative polarity where the bacterial population reduction reached up to 2.2 logs at 10 min exposure time.

Numerical simulation of Trichel pulse characteristics in bar-plate DC negative corona discharge

An improved multi-component two-dimensional hybrid model is presented for the simulation of Trichel pulse corona discharge. The model is based on the plasma hydrodynamics and chemical models, including 12 species and 27 reactions. In addition, the photoionization and secondary electron emission effects are taken into account. Simulation is carried out on a bar-plate electrode configuration with an inter-electrode gap of 3.3 mm, the positive potential applied to the bar being 5.0 kV, the pressure in air discharge being fixed at 1.0 atm, and the gas temperature assumed to be a constant (300 K). In this paper, some key microscopic characteristics such as electric field distribution, net charge density distribution, electron density distribution at 5 different instants during a Trichel pulse are analyzed emphatically. Further more, the electron generation and disappearing rates, positive and negative ion distribution characteristics along the axis of symmetry are also investigated in detail in the later Trichel pulse cycle. The results can give valuable insights into the physical mechanism of negative corona discharge.

Onset voltage of a particle-initiated negative corona in a co-axial cylindrical configuration

This paper presents a theoretical and experimental study of the effect of conducting particles on the onset voltage of a negative corona in air-insulated co-axial cylindrical configurations. The conducting particles are spheres or wires of varying dimensions. The particle is fixed either on the inner or the outer cylinder. The calculated onset voltage of the negative corona is based on the criterion developed for the formation of repetitive negative coronas, Trichel pulses. This calls first for an accurate calculation of the electric field in the vicinity of the particle where avalanches grow. The investigated gap in the presence of a particle is a three-dimensional field problem due to the asymmetrical position of the particle inside the gap. The three-dimensional electric field is calculated using the charge simulation technique with a new charge distribution. An experimental set-up is built up to measure the onset voltage of a negative corona initiated by particles in an air-insulated co-axial configuration to check the accuracy of the present calculation. The effect of varying field nonuniformity, particle shape, size and position on the onset voltage of the negative corona is investigated. The calculated onset voltage values agree well with those measured experimentally.

High-resolution measurements of the electric field at the streamer arrival to the cathode: A unification of the streamer-initiated gas-breakdown mechanism

A time-correlated single-photon counting technique was used to verify the formation of a cathode-directed streamer inside the narrow cathode region following the interpulse phase of regular negative corona Trichel pulses in ambient air. A purely experimental approach was used to determine the spatiotemporal development of the electric field during the Trichel pulse rise with an extremely high resolution of 10 μm and tens of picoseconds. The results confirm the positive-streamer mechanism for Trichel pulse formation and provide supportive evidence for the hypothesis that the formation of a primary cathode-directed streamer occurs always in any streamer-initiated breakdown and prebreakdown phenomena associated with cathode spot formation.

Research on Electrical Characteristics of Dielectric Barrier Discharge and Dielectric Barrier Corona Discharge

The dielectric barrier corona discharge (DBCD) in a wire-cylinder configuration and the dielectric barrier discharge (DBD) in a coaxial cylinder configuration are studied. The discharge current in DBD has higher pulse amplitude than in DBCD. The dissipated power and the gas gap voltage are calculated by analyzing the measured Lissajous figure. DBCD has lower gas gap breakdown voltage. The average electric field is about 10–20 kV/cm in gas gap during DBCD, and is 30–40 kV/cm during DBD. In the positive half cycle the DBCD appears as continuous discharge current mode and in negative half cycle it appears as Trichel pulse mode. Under some conditions DBCD can show homogeneous diffuse discharges mode.