Numerical Investigation On The Typical Nonlinear Phenomena In Helium Dielectric Barrier Discharges At Atmospheric Pressure

Atmospheric pressure dielectric barrier discharge(APDBD),being one of the most commonly used schemes for low-temperature plasma generation,has received much attention from scientists and engineers of various fields in recent decades due to its promising perspective in biomedical treatment,material processing,surface modification,pollution abatement,etc.Owing to the inborn nonlinear characteristics,APDBD systems are always rich in nonlinear phenomena,while the in-depth initial mechanisms of those phenomena are far from being understood at the moment.To uncover some subtle mechanisms related to the generation and evolution of nonlinear behaviors in APDBDs,realize the manipulation of discharge dynamics states,and thus mitigate the negative effects of nonlinear discharges on pratical plasma applications,a systematic study concerning this issue was performed and recorded in this paper,whose main content is listed as follows:(1)Based on the practical geometry of parallel plate dual-barrier APDBD,fluid models with one-dimensional and two-dimensional geometric sketches were established,and qualitative validity of those models were verified by comparing the simulation results with those obtained in previous experiments.Furthermore,by properly adjusting the operating parameters in relatively wide ranges,the evolution trajectories of typical nonlinear phenomena(i.e.asymmetric single-period state,multi-periodic state,period-doubling bifurcation,multiplecurrent-pulse discharge,patterned discharge)were traced and recorded in the study.(2)To uncover the mechanisms behind the observed phenomena,this work focused on the discharge cases in the vicinity of nonlinear mode transition points.By scrutinizing the macro electrical characteristics(e.g.current density,peak phase,number of pulses per half cycle)as well as the micro parameters(e.g.seed electron level,ionization rate,width of plasma column)in those discharge cases,some unexplored insights regarding the transition between symmetric single-period state and asymmetric single-period state,the period-doubling bifurcation,the transition between single-current-pulse mode and multiple-current-pulse mode,the conversion from stationary discharge pattern to complementary discharge pattern etc.in APDBDs were obtained.Through the effort made in this work,a series of new understandings concerning the nonlinear phenomena in APDBDs were revealed.In particular,the critical role of electron backflow process in initiating the discharge asymmetry was substantiated,the importance of transient evolution process in determining the discharge state was emphasized,the merging process of pulses in multi-pulse mode was interpreted from the angle of discharge current component,and the role of pre-ionization level in initiating the complementary patterned discharge mode were verified.Those discoveries expanded people's horizons in the area of nonlinear discharge dynamics,and promoted the development of practical plasma applications in relevant industrial fields.