Research On The Characteristics And Mechanism Of Periodic Symmetrical Gaussian Voltage Driving Atmospheric Pressure Dielectric Barrier Discharge

Atmospheric pressure(AP)low temperature dielectric barrier discharge(DBD)plasmas have been of an enormous interest owing to their attractive characteristics that make them indispensable in a variety of advanced applications including surface treatment of polymers,industrial ozone generation,biological sterilizing,air purification,etc.In the past several decades,people were devoted to the much lower power consumption,higher plasma-chemical efficiency,and much better uniform atmospheric pressure dielectric barrier discharge plasma.The power resource is a key factor to influence the characteristics of discharge.Characterized by a short duration time and a fast rising time,Gaussian discharge can input much more energy in generating energetic electrons instead of heating the background working gas.Hence,it exhibits many unique advantages and unprecedented potentials than sinusoidal alternating current discharge.In view of this,we proceed with the theory and simulation studies on the characteristics and the mechanisms of dielectric barrier discharge excited by Gaussian discharge at atmospheric pressure.The specific research contents and related results are shown as follows.Firstly,based on a one-dimensional(1D)self-consistent fluid model,we carry out a systematic comparison study about the difference between two types of discharges involved in Gaussian and sinusoidal voltages through the voltage waveform,the intensity of electric filed,electron temperature,discharge power consumption,and active species,et al.,and detailedly analyze and discuss the physical mechanisms behind Gaussian and sinusoidal discharges.Research results show that,in the Gaussian and sinusoidal discharges with multi-pulse,a transition between the Townsend mode and glow one exists during the half-cycles of both their voltages.Gaussian discharge exhibits more distinct advantages in the aspect of a higher plasma-chemical efficiency under the circumstance of much lower power consumption as compared to the sinusoidal discharge.Secondly,we use a 1D self-consistent fluid model to investigate the characteristics of atmospheric-pressure argon dielectric barrier discharge excited by periodic Gaussian voltage.With the driving frequency,voltage amplitude,and gas gap set at certain values,the temporal evolutions of discharge current density and gas voltage are obtained,together with the spatial distributions of electron and ion densities and electric field.Simulation results indicate that there are two discharge modes:Townsend and glow modes in the multi-current pulse discharge excited by Gaussian voltage.A mutual transition between the Townsend mode and glow one occurs during each half cycle of the applied voltage,which is attributed to the space charges in the gas gap and the surface charges on the dielectrics.Additionally,a residual current peak is observed during the falling phase of each half cycle.This is resulted from the fact that amounts of space charges are trapped in the gas gap during the rising phase of the applied Gaussian voltage.Thirdly,a 1D self-consistent fluid model was also used to investigate the effect of driving frequency on the characteristics of dielectric barrier discharge at atmospheric pressure in argon excited by a periodic Gaussian voltage.When the driving frequency is 1 kHz,there is a tendency of transition from the Townsend mode through glow and finally back to the Townsend one during the positive half-cycle of applied Gaussian voltage.However,the discharge in the half-cycle can all along operate in the glow mode with the higher driving frequency.Moreover,when the driving frequency is sufficiently high,there are also distinct fluctuations of spatial performance of the charge densities in the positive column during the glow discharge.This is caused by the fact that a lot of charged particles created in the gas gap have not enough time to drift and diffuse to the dielectric barriers,and then these particles are preserved in the local discharge gap at such a high frequency.The 1D comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increase in the driving frequency can enhance the plasma chemistry activity.Finally,a two-dimensional(2D)self-consistent fluid model was employed to investigate the spatiotemporal characteristics of atmospheric pressure argon(Ar)dielectric barrier discharge(DBD)driven by a Gaussian voltage.A transition from Townsend mode to glow mode is observed with the increasing applied voltage each half-cycle at a lower driving frequency(7.5 kHz).It is also found that the glow mode survives all the discharge phase at a higher driving frequency(12.5 kHz and 40 kHz).The change of discharge mode with the driving frequency mainly lies in the fact that a lot of charged particles created in the discharge gap have no enough time to drift and diffuse around to be lost.Additionally,the spatial distributions of the electron density indicate that a center-advantage discharge is ignited at the driving frequencies of interest,resulting in the radial non-uniformity of discharge because of the edge effects.However,this overall non-uniformity is weakened with the increasing driving frequency.These distinct behaviors are mainly attributed to the fact that many charged particles generated are trapped and then accumulated to make the extension along the radial direction in the glow discharge due to the charged particles transport and diffusion,and that the effective overlapping of a large number of avalanches induced by the increased 'seed'electron density,i.e.the electron density remaining from the previous discharge pulse,is one important mechanism for reducing the radial non-uniformity and for leading to a uniform glow discharge at atmospheric pressure.The 2D comparison of the spatiotemporal evolutions of the electron density at different driving frequencies indicates that the increase in the driving frequency can enhance the plasma chemistry activity and improve its uniformity.The physical mechanism and electric characteristics of atmospheric pressure argon DBD excited by Gaussian voltage have been investigated and discussed by employing the numerical simulations based on 1D and 2D self-consistent fluid model as mentioned above.Not only does this work rich and improve a theoretical model of atmospheric pressure DBD,but also its solid theoretical foundation can be widely used to design the excitation resources of discharge configuration generator and optimize operating-parameter control strategy for the high efficiency,low power plasma,and provide a novel technical guidance for the practical application of atmospheric pressure DBD in the fields of surface modification,industrial ozone generation,biological sterilization,and air purification,et al.