Influence of air impurities on the transition from a symmetric discharge to an asymmetric discharge in an atmospheric pressure helium diffuse dielectric barrier discharge

Abstract

The transition from a symmetric and single period (SP1) discharge to an asymmetric and single period (AP1) discharge is a typical nonlinear dynamical phenomenon in dielectric barrier discharges (DBDs) at atmospheric pressure. Considering the presence of air impurities in practical applications which is always unavoidable due to the air-tightness of the DBD reactor, a one-dimensional fluid model with 26 species and 154 reactions is developed to thoroughly investigate the influence of air impurities on the transition from the SP1 discharge to the AP1 one in atmospheric DBDs in a helium mixture with air impurities. In our study case, simulation results show that the discharge experiences the transitions from the SP1 discharge to the AP1 one twice when the air impurity content is increased from 1 to 200 ppm. The first transition (appearing around 60–100 ppm) is due to the additional pre-ionization electrons generated by the higher rate of Penning ionization in the pre-ionization phase, whereas the second transition (occurring around 170–200 ppm) is due to the reduction of the residual electron density which is caused by the decrease in the electron production rates and the change in applied voltage polarity. In addition, as the air impurity content exceeds a certain amount, the rates of Penning ionization are the result of the competition between the increase in the mole fractions of N2 and O2 and the decrease in the molar fractions of He* and He2*.