Research On Columnar Discharge Between Parallel Dielectric Barrier Electrodes In Atmospheric Helium

Cold plasma has been the research hotspot of scholars because of its great application prospect.Dielectric barrier discharge is one of the main ways to produce cold plasma,with the advantages of high efficiency and convenient.But the dielectric barrier discharge is also a complex nonlinear dynamic process that the discharge process involves complex physical and chemical change.And it is very sensitive to the variation of external parameters,and presents different discharge modes under different conditions.Thus,to study the formation mechanism of different discharge modes is of great significance for the production,stability and controlling of the cold plasma.Aiming at dielectric barrier columnar discharges in atmospheric helium,a model of the dielectric barrier discharge was established using the COMSOL software.By combining simulation results with experimental data,an in-depth analysis of the formation mechanism,the dynamic characteristics and influencing factors of columnar discharge was carried out,and the transition between columnar discharge and uniform discharge was also discussed.The main contents are as follows:1)Based on the COMSOL simulation software,a two-dimensional(2D)axisymmetric fluid model of the plate electrodes dielectric barrier discharge was established,and a comparison analysis of the performance of two main algorithms(the finite element method and finite volume method)and their influence on the simulation results under different mesh structures was implemented.Validation of the simulation model was verified by comparing the calculated current waveform,the 2D electron density distribution of columnar discharges with the experimental results.2)Using the 2D axisymmetric model,the physical process of the formation of columnar discharges in atmospheric helium and the electric field distribution of discharge column were analyzed.First,through the calculated distribution of electron density,discharge current and distribution of equipotential lines during the discharge,the formation mechanism of columnar discharge was analyzed deeply.Second,based on the 2D distribution of equipotential lines,the distribution of radial electric field around the discharge column was calculated and analyzed.It was found that this radial electric field has an inhibiting effect on the discharge in the peripheral area.3)Based on the 2D axisymmetric simulation model,the dynamic characteristics of the columnar discharge during its decay were studied.First,time evolutions of the charged particles were analyzed through the calculated 2D distributions of the charged particles,waveforms of applied voltage and discharge current.It was found that new Townsend discharges occur at the nondischarge-column locations after the extinction of the discharge columns.Second,time evolution of the axial electric field was studied according to the distributions of equipotential lines and surface charge density.It was found that alternating inverted axial electric field is formed in the gap after the extinction of the discharge columns.Finally,the distribution and time evolution of the surface charge accumulated on the dielectics were calculated and analyzed,and the changing laws of the surface charge at discharge-column locations and nondischarge-column locations were obtained.4)Influence of the variation of discharge parameters on the columnar discharge was studied,and the transition between columnar discharge and uniform glow discharge was discussed.First,the influence of the applied voltage amplitude,frequency,and the discharge gap distance on the columnar discharge was was studied by experiment,and the influence rule of these parameters on the columnar discharge were obtained.Second,the influence of N2 impurity on the columnar discharge was analyzed through the simulation model,and it was found that the discharge tends to be uniform glow discharge after adding a certain amount of impurities.