Trichel pulse of negative corona discharge in atmospheric air is investigated numerically using a 2D fluid model. The model consists of a hyperbolic cathode tip and a plane anode, and considers 11 ...kinds of particles and the most important interactions among them. The spatio-temporal evolution of charged species and the electric field are evaluated during the pulse process. During the pulse rising edge, the positive ions accumulate ahead of the tip forming the temporal cathode sheath, significantly enhancing the local field. In the pulse decay edge, the temporal sheath collapses and the discharge falls back to a low-current mode. In the pulse interval, the discharge does not cease but sustains weakly until the next pulse. The location of the temporal sheath is independent of the averaged value during the Trichel pulse regime and also the same with that in a normal glow regime, which determines a nearly constant pulse rising time at given configurations. However, a smaller tip radius will lead to their decrease. The effect of negative ions on the pulse process is studied by adjusting the attachment rates. It indicates that the negative ions are actually not necessary in the Trichel pulse process, but will influence the pulse waveform significantly.
The uniform gas discharge has long been pursued for realizing or improving some practical applications but is difficult to achieve due to the fact that nonuniform discharges are much easier to be ...generated in most cases. Usually, achieving uniform gas discharge requires sophisticated devices, and the operation is complicated and time-consuming. In this paper, we introduce simple and flexible multimethods for realizing uniform discharge from patterned structures under dielectric-barrier discharge (DBD) systems by varying experimental controlling parameters, and these methods can be employed in combination. The effects of driving frequency, voltage, duty ratio, and magnetic/electric field on glow DBD structure are investigated. It is found that a uniform glow DBD is obtained when frequency, voltage, and duty ratio are either very high or very low and also by the introduction of strong magnetic/electric field. The underlying physics of these methods is consistent as the elimination of a focusing effect of space electrons. It is concluded that the key of achieving uniform discharge is to uniformize the distribution of space charges.
During a dc corona discharge, the ions’ momentum will be transferred to the surrounding neutral molecules, inducing an ionic wind. The characteristics of corona discharge and the induced ionic wind ...are investigated experimentally and numerically under different polarities using a needle-to-ring electrode configuration. The morphology and mechanism of corona discharge, as well as the characteristics and mechanism of the ionic wind, are different when the needle serves as cathode or anode. Under the different polarities of the applied voltage, the ionic wind velocity has a linear relation with the overvoltage. The ionic wind is stronger but has a smaller active region for positive corona compared to that for negative corona under a similar condition. The involved physics are analyzed by theoretical deduction as well as simulation using a fluid model. The ionic wind of negative corona is mainly affected by negative ions. The discharge channel has a dispersed feature due to the dispersed field, and therefore the ionic wind has a larger active area. The ionic wind of positive corona is mainly affected by positive ions. The discharge develops in streamer mode, leading to a stronger ionic wind but a lower active area.
In this paper, we report the experimental results on the characteristics of plasma patterns with different planar electrode shapes in dielectric barrier glow discharge. The formation and the ...evolution of the discharge patterns at different voltages were investigated. The results show that the plasma patterns in this glow-barrier system form at the beginning of the discharge pulse. The limited size of planar electrodes and the electric field distribution are important factors for the pattern formation.
The spatio-temporal characteristics of microhollow cathode sustained discharge are investigated using a fully self-consistent fluid model. The evolutions of discharge current, electric potential, ...electron density, the axial and radial electric fields, and ionization rates are simulated at 100 Torr. The interaction between the microhollow cathode discharge (MHCD) and the microhollow cathode sustained discharge (MCSD) is also investigated. Results show that the mode transition is related to the distance d between the first anode and the second anode. When the distance is large (e.g. d = 2 mm), a complete discharge process comprises five stages. These stages are Townsend mode, the transition from mainly axial electric field to mainly radial electric field, the formation of the hollow cathode effect, the formation of microcathode sustained discharge, and stable discharge. The influence of MHCD on MCSD is prior to the influence of MCSD on MHCD. By contrast, when d is very small (e.g. d = 0.3 mm), the influence of MHCD on MCSD is posterior to the influence of MCSD on MHCD.
This paper deals with an experimental study of a copper wire explosion in air and water at atmospheric pressure. The influence of the stored energy, discharge type, ambient medium on the electrical ...and optical characteristics of a single wire explosion was examined and clarified. Particularly, optical emission spectroscopy as well as self-emission image diagnosis were conducted to understand the radiant and quenching process of the explosion. The results revealed that the radiation mainly contained two stages: a white light (continuous spectrum) flash soon after the moment of explosion, and a long period of line radiation of Cu ions/atoms in the following dozens of microseconds. By analysing characteristic lines, Cu2+ was found in the very early stage of the expansion of the discharge channel (DC). Besides, obvious line radiation of O and N ions/atoms was found when there existed a current pause. As for plasma parameters, the Boltzmann plot method indicated that the average temperature of explosion products was ∼1 eV, while the electron density experienced an apparent attenuation as the expansion of DC. In addition to this, the optical emission in air and water followed two distinctly different patterns, relating to the expansion of DC and diffusion of the ambient medium.
In this paper, an ion source based on wire-to-plate corona is developed for Ion Mobility Spectrometer (IMS). The characteristics of the corona discharge and the ion current detected on Faraday plate ...are investigated under different electrode spacing and voltage. The effect of voltage polarity is also studied. The features of this new designed ion source are compared with that of point-to-plate corona. The results show that the present IMS prototype machine can provide a much larger value of ion current connected by Faraday plate than the point-to-plate corona and/or the traditional 63Ni source. The corona configuration can also act as a good electromagnetic shielding to defense the electromagnetic emission from the corona discharge.
Conductive solid material sampling by micro-plasma under ambient atmosphere was studied experimentally. A high-voltage pulse generator was utilized to drive discharge between a tungsten needle and ...metal samples. The effects of pulse width on discharge, micro-plasma and sampling were investigated. The electrical results show that two discharge current pulses can be formed in one voltage pulse. The duration of the first current pulse is of the order of 100 ns. The duration of the second current pulse depends on the width of the voltage pulse. The electrical results also show that arc micro-plasma was generated during both current pulses. The results of the emission spectra of different sampled materials indicate that the relative emission intensity of elemental metal ions will increase with pulse width. The excitation temperature and electron density of the arc micro-plasmas increase with the voltage pulse width, which contributes to the increase of relative emission intensity of metal ions. The optical images and energy dispersive spectroscopy results of the sampling spots on metal surfaces indicate that discharge with a short voltage pulse can generate a small sputtering crater.
In this paper we report the semi-conductor of zinc oxide (ZnO) thin film deposited by reactive high power impulse magnetron sputtering (R-HiPIMS) on glass substrates without external heating. We ...focus on the influence of deposition parameter, the ratio of O2/Ar exactly, on the crystalline and electrical properties of ZnO films. It is found that n-type ZnO film with a high carrier concentration can be grown through HiPIMS technique, the ratio of O2/Ar remarkably affects the ZnO crystalline and electrical properties. At O2/Ar = 14/80 sccm, the ZnO film was orientated at c-axis (002) plane. Based on the temporal resolution optical emission spectroscopy (OES), for the proposal of the correlation of film structure with plasma radicals and the reaction process in ZnO growth, the components in plasma are diagnosed. It is concluded that in a higher oxygen partial pressure, owing to the high ionization rate in HiPIMS, the oxide layer formed between pulses is removed, the growth of a new oxide layer during the pulse is hindered, hence the growth rate is increased, and the carrier concentration caused from point defects in ZnO film is high.
•The nucleation and coalescence of ZnO are correlation to O2/Ar ratio.•With increase of O2/Ar ratio, the densities of Ar+ and Zn+ were increased.•The Penning discharge happens in the HiPIMS.
