Non-thermal air plasma jets at atmospheric pressure: The flow-dependent propagation in the afterglow

Abstract

With a bare pin-to-nozzle electrode configuration, an ac-driven non-thermal air plasma jet with a length of several centimeters is generated. Depending on the gas flow rate, the propagation speed of these plasma columns is in the range of 100–350 m/s, which is close to the gas flow velocity. This indicates that the propagation of the plasma jet is determined by the transport of long lifetime species by gas flow instead of the electron-impact excitation and ionization of molecules under a high electric field. In comparison to the N2, O2, and Ar plasma jets, the length of the air plasma jet is much shorter than that of the N2 plasma jet but longer than that of the O2 and Ar plasma jets. A simple kinetic model reveals that the N2 (A3Σ) metastable plays a crucial role in sustaining the length of the N2 and air plasma jets, whose lifetime is strongly dependent on the quenching effect of O2, O, and NO as well as the compensation from the three-body recombination of nitrogen atoms. Based on the flow-dependent mechanism of the plasma jet, a visually uniform air plasma brush with a width of 2.8 cm and a length of 1.6 cm and a visually uniform N2 plasma brush with a width of 4 cm and a length of 4.4 cm have been demonstrated.