Comparison of formation mechanism between helium and argon atmospheric pressure plasma jets

To compare the formation mechanisms of He and Ar atmospheric pressure plasma jets (APPJs), an intensified charge-coupled device (ICCD) are utilized to observe the dynamic process of APPJ. The experimental results show that, He APPJ is first ignited, which is independent of the dielectric barrier discharge (DBD) between the two wrapped electrodes when the high voltage placed at the downstream. The intensity and APPJ length under positive discharge pulses are bigger than that under negative discharge pulses due to the space charge effect. The He APPJ is formed by the DBD development when the high-voltage electrode placed at the upstream side of tube. However, the plasma plume in Ar APPJ is formed by the propagation of DBD whatever the high-voltage electrode is arranged on upstream or downstream side of ground electrode. The difference in formation mechanism between He and Ar APPJs is mainly caused by the gas properties. Moreover, during the discharges, Ar tends to lead to thermal instability and electron Maxwellian instability.