Simulation On Mechanism And Characteristics Of Dielectric Barrier Discharge With Ring Electrode In Atmospheric Helium

In recent years,cold plasma technology has been greatly developed due to its wide applications in thin film deposition,surface modification,ozone generation,biomedicine,pollution abatement and other industries.Dielectric barrier discharge(DBD),as one of the main methods for generating cold plasma at atmospheric pressure,has become a research hotspot due to its simple discharge structure,avoidance of transition to arc discharge,and easy generation of large-volume and high-density plasma.However,when processing small or irregular samples(such as ring samples)in practical applications,the traditional DBD with parallel-plate electrode has the following disadvantages: energy waste and low utilization.In order to solve the above problems,the simulation study of the DBD equipped with ring electrode at atmospheric pressure is carried out using the representative ring-shaped sample as the research object to explore the evolution law of the discharge phenomenon and the physical mechanism behind it,and to achieve parameter adjustment of the DBD to obtain a locally concentrated and highly active plasma.So as to solve the problems of energy waste and low plasma utilization in irregular sample processing.This paper not only establishes a two-dimensional model of the atmospheric helium DBD equipped with ring electrodes,but also calculates the temporal evolution of the discharge current,current density,and the spatial distribution of the electron density,electric field,surface charge and stationary DC electric field.Moreover,the discharge power under different electrode geometries is compared,and the discharge characteristics are investigated.It provides a theoretical basis and technical support for rationally optimizing the electrode structure according to sample structure,processing samples more accurately and efficiently,and improving the utilization of plasma.The main research works include four aspects:1)Based on the two-dimensional self-consistent fluid model and numerical simulation,the single pulse discharge characteristics of the DBD with ring electrode in atmospheric helium are studied.The temporal evolution of current,current density,total capacitive power deposition during the discharge,as well as the spatial distribution and evolution of electron density,electric field and surface charge density are given.The discharge characteristics of the DBD with ring electrode and the DBD with parallel-plate electrode are compared and the difference is clarified.The results show that when the electrode changed from parallel-plate to ring,the electron density magnitude remains unchanged,and the energy consumption is reduced to 88.7% of the DBD with parallel-plate electrode.2)The multi-pulse discharge characteristics of DBD with ring electrode are further theoretically studied by the two-dimensional self-consistent fluid model.It is found that for multi-pulse discharge,the breakdown position of adjacent discharge pulses alternates between the center and the periphery of the ring electrode,and the spatial distribution of electron density at peak moment also exhibits alternating feature between the center-advantage and periphery-advantage.Through the analysis of the radial distribution of surface charge,it is revealed that the uneven distribution of surface charge during the last discharge is the key factor leading to the alternating behavior.3)The discharge characteristics of DBD with double-ring electrodes in atmospheric helium are studied and the influence of electrode arrangement on the spatial distribution of electron density is explored by the two-dimensional self-consistent fluid model.It is found that the when electrode arrangement changes,the periodic alternating and complementary characteristics of spatial distribution of electron density change accordingly.It is compared and learned that uneven distribution of electric field and surface charge directly leads to the alternation of the spatial distribution of electron density.The results show that the difference in the stationary DC electric field distribution in gas gap determined by the different arrangement of electrodes is the fundamental reason for the different spatial distribution of electron density.4)The discharge characteristics of DBD with asymmetric electrode in atmospheric helium are studied by the two-dimensional self-consistent fluid model.It is found that the asymmetry of electrodes lead to the symmetry of the discharge current pulse in the positive and negative half cycles and the complementary behavior of the spatial distributions of the electron density and electric field disappear.The stationary DC electric field distribution in the discharge space is analyzed,and it is revealed that the curtain-like distribution of the radial electric field near the upper dielectric layer is caused by the uneven distribution of surface charge and the asymmetry of the electrodes.The results show that when the electrode changes from symmetric ring to asymmetric one,the magnitude of electron density remains unchanged,and the energy consumption is reduced to 48.7% of the DBD with symmetric ring electrode.