Study On The Transition Mechanism And Stability Of Spatial Discharge Modes In Atmospheric Helium Dielectric Barrier Discharges

Dielectric barrier discharge(DBD)is a typical non-equilibrium dissipative system.The variation of applied parameters makes it undergo mode transitions between uniform and columnar discharges,and possibly induces self-organized behaviors.However,the current understanding of such phenomena is still very limited.In order to reveal the underlying transient evolution mechanism,understand the destabilization of the uniform steady-state,and efficiently regulate DBD’s spatial uniformity,this paper takes atmospheric helium(He)parallel-plate DBD as the research object,and uses plasma fluid simulation,supplemented by pattern dynamics analysis and experimental verification,to carry out the following work:1)The effects of applied voltage amplitude and gap width were discussed.Based on the qualitative agreement between the simulation and experimental results,the transition law of space discharge modes and the underlying mechanism are obtained by analyzing the transient evolution process.Increasing the voltage amplitude will make the initial surface charge distribution and the subsequent seed electron distribution more uniform,which is helpful to expand the discharge area,increase the discharge column and improve the discharge uniformity;The effect of enlarging gap width on spatial discharge modes is nonlinear.On the one hand,it can promote the formation of the discharge column by strengthening the electron avalanche;on the other hand,it may also lead to incomplete discharge dissipation and strong surface charge neutralization,which limits the activation-inhibition effect and maintains the DBD in the quasiuniform mode.2)The influence of air impurities,which is arguably unavoidable in experiments and practical applications,is discussed.Different from the previous simplified model containing only nitrogen impurities,this study considers additionally doped oxygen and verifies the model by quantitative comparison with the experimental voltage and current waveforms.The research reveals the transition mechanism of DBD’s spatial discharge modes under the variation of impurity content.The rise of impurity level will strengthen Penning ionization and promote the gap breakdown.A stronger breakdown is apt to cause the activation-inhibition effect and lead to the formation of discharge columns,but a faster breakdown may cause multi-pulse phenomenon and complementary discharge characteristics,which hinders the establishment of surface charge memory effect and maintains the DBD in the quasi-uniform mode.furthermore,compared with the results calculated from the simplified model containing only nitrogen impurities,this study substantiates that the additionally doped oxygen will affect the discharge mechanism from the electron adsorption and complementary characteristics,and the seed electron density is not the only indicator for evaluating discharge uniformity.3)The wavy dielectric surface is purposely built for imitating the non-smooth targeted object surface that DBD may encounter in practical applications.The simulation results show that even inconspicuous surface fluctuation can destroy the discharge uniformity,which is consistent with the fact that columnar discharge is often observed in practical applications.The study reveals the inducing effect of surface fluctuation on the fast emergence of columnar mode that is,the radial discrepancy of gap width will lead to local accumulation of seed electrons before the breakdown,which can cause the simultaneous formation of discrete columns at the first breakdown.Meanwhile,the local electric field distortion near the wavy dielectric surface will further change the concentration areas of seed electrons at the positive and negative breakdowns’ pre-ionization stages,so that the complementary characteristic appears.4)Based on the plasma fluid model of He parallel-plate DBD,a simplified reactiondiffusion equation is formed Through linear stability analysis,the instability criterion of uniform steady-state and the corresponding vital intrinsic parameters are obtained,that is,the axis-averaged electric field intensity and seed charge density at the pre-ionization stage.The increase of the former and the decrease of the latter both contribute to the formation of columnar mode.The exploration of the system destabilization is helpful to connect the influence of different external parameters on DBD’s spatial discharge modes.On this basis,this study proposes a new idea of regulating discharge uniformity by using clipping voltage to tune the discharge dissipation.The feasibility of this method is that it can limit the activation-inhibition effect and surface charge memory effect without significantly affecting the discharge current,and this method can improve the discharge efficiency.This study may enrich and deepen people’s understanding of the spatial discharge mode transition and self-organized behaviors in DBD,and also provides a reference for the subsequent theoretical and practical research.