Influence of electron backflow on discharge asymmetry in atmospheric helium dielectric barrier discharges

In this paper, the transition mechanisms between symmetric and asymmetric discharges in atmospheric helium dielectric barrier discharges (DBDs) are investigated via a one-dimensional fluid model. By gradually increasing the gap width, a complete evolution trajectory of the discharge states (i.e. from symmetric single period discharge (SP1) to asymmetric single-period (API) discharge, finally returns back to SP1 discharge) is observed. Unlike the previous reports which emphasize the dominant role of residual positive column, this work demonstrates that the transitions between SP1 and AP1 discharges could also be induced by the electron backflow effect. It is the residual electron backflow region that provides extra seed electrons to the subsequent discharge, restraining the development of electric field in the breakdown process, thus weakening the next discharge pulse. Upon the impairment of one discharge pulse, due to the reduction of charge generation and the impairment of electron backflow effect in the relevant discharge phase, its subsequent discharge would be strengthened. Those mechanisms function in different current pulses at different gap widths, inducing the mode transition. In addition, our simulation result reveals that the "residual positive column" referred in previous publications is essentially a special form of the "electron backflow region", which is typically more remarkable in large gap widths. As a consequence, the dynamics of electron backflow provides more insights regarding the transition of nonlinear states in DBDs with controlling parameters varying. (C) 2018 Author(s).