Numerical Simulation Of Uniform Discharge Excited By Direct And Saw-tooth Voltage At Atmospheric Pressure

Recently,the low temperature plasma are widely used in industrial applications,so that the development of the low temperature plasma generated by gas discharge under atmospheric pressure has become one of the most attractive researches in the field of gas discharge and non-thermal plasma.Direct current(DC)discharge is one of the easy methods of generating low temperature plasma and the dielectric barrier discharge(DBD)is a traditional way for initiating low temperature plasma.In this paper,the low temperature plasma generated by DC discharge and DBD have been investigated in detail through fluid simulation.The time evolution of the total current density and the voltage,as well as the space and time distribution of the electric field and the electron,the ion densities are calculated by solving the one-dimensional continuity equation.The characteristics of atmospheric uniform discharge are investigated numerically generated by DC discharge and a DBD excited by a saw-tooth voltage.The main simulation results are listed as follows.(1)the characteristics of DC discharge in atmospheric pressure have been investigated.Results indicate that it takes a period of time before the discharge reaches its steady state.Moreover,the needed time increases,and the current density of the steady state decreases with increasing the gap width.Through analyzing the spatial distributions of the electron density,the ion density and the electric field at different discharge moments,it is found that the DC discharge starts with the Townsend regime,then transits to the glow regime.The discharge operates in a normal glow mode a narrower gas gap(2mm)and larger ballast resistor(200k?and300k?).For a wider gap(4mm and 10mm)or smaller resistor(100k?),the discharge operates in an abnormal glow mode.It is also found that the discharge always operates in an abnormal glow mode with a small variance of the secondary electron emission coefficient.(2)The influence of frequency on discharge modes in a dielectric barrier discharge excited by saw-tooth voltage have been numerically investigated in atmospheric argon.Results show that the discharge mode transits from APTD to APGD with the frequency increasing under the same external voltage amplitude.The discharge current shows a broad plateau per half cycle of the applied voltage when frequency is smaller.As the frequency increases,the amplitude increases and the width decreases of the plateau.In addition,the current of the stepped discharge consists of some pulses superimposed on the plateau when frequency is increased tosome extent.Compared with the stepped discharge with small f,pulsed discharge is obtained with large frequency.Through analyzing the spatial distributions of the electron density,the ion density and the electric field at different discharge moments,it is found that the stepped discharge belongs to the Townsend mechanism,while the pulsed discharge belongs to the glow mechanism.