Dynamic Simulation Of Micro-hollow Cathode Discharge And Dielectric Barrier Discharge At High Pressure

As a typical high pressure discharge,the micro hollow cathode discharge can produce a high concentration of dense plasma at a lower discharge voltage.It is widely used in film deposition,large-scale discharge,sterilization,electromagnetic wave absorption and other fields.In this paper,a two-dimensional fluid model is used to calculate the situation when the micro-hollow cathode discharge covered by the dielectric on the outer cathode.The main conclusions are as follows:The discharge evolution process is divided into Townsend preionization phase,streamer mode and glow mode.The electron density,ion density and current intensity are low during the Townsend preionization phase.The plasma propagates along the wall near the cathode and a charge separation process occurs in the anode pore.During the streamer propagation phase,the streamer arises and travels forward within the anode hole,and subsequently travels along the wall.During the glow mode phase,the discharge has entered the cathode hole and formed the cathode sheath structure.By comparing the voltammetry characteristics,it is found that the traditional micro-hollow cathode discharge is first in the abnormal glow mode,and it changes to the glow mode as the current increases.However,the micro-hollow cathode discharge which the cathode outer surface is covered by a dielectric plate(c-MHCD)always be in the abnormal glow mode.When changing the discharge parameters,the conclusions are as follows:(1)As the inner diameter of the discharge cavity increases,the electron density in the cavity gradually decreases.In addition,as the aperture increases,the plasma travels along the wall’s behavior also gradually weaken,but the discharge current at the steady state gradually increases.The variation in the aperture has little effect on the cathode sheath thickness.(2)With the increase of pressure,the electron density and the discharge current gradually decreases.In addition,the electron density in the cathode cavity decreases more significantly,and the distribution of the plasma in the cathode is also more "expanded",and the thickness of the cathode sheath gradually decreases.(3)As the thickness of the intermediate dielectric layer increases,the density of the plasma and the discharge current decreases,but the cathode sheath thickness increases.In the intermediate layer thickness(less than 0.2 mm),plasma propagation along the wall.Continuing to increase the thickness of the dielectric layer,the propagation behavior along the wall occurs before the streamer enters the cathode hole.(4)When the cathode thickness is changed,the discharge current and the average electron density in the cavity are almost constant.There is no difference in the cathode sheath thickness or the depth of the plasma into the cathode。In addition,the influence of applied voltage asymmetry on uniform dielectric barrier discharge characteristics of atmospheric helium gas is studied by one-dimensional fluid model.Based on the standard sinusoidal waveform,an asymmetric sinusoidal voltage is obtained by increasing or decreasing the proportion of voltage rise time in each half cycle.The simulation results show that the discharge current density and electron density can be increased significantly with the increase of the level of asymmetry,and the duration of high electron density also increases obviously.In addition,the current peak phase gradually approaches the zero of the applied voltage,and the discharge mode changes from Townsend mode to glow mode.During this period,the main pathway of electron production-Penning ionization was gradually replaced by direct ionization.