Study on discharge mode and transition mechanism of atmospheric pressure Ar/Zn pulsed microwave plasma jet

The microwave plasma jet has the advantage of high plasma density and abundant active particles but fails to produce large-scale microwave plasmas in ambient air which hinders the application of microwave plasma ignition and combustion. We have applied a surface wave resonator (including a Zn-coated iron wire trigger) to produce a large-scale Ar/Zn pulsed microwave plasma jet. The discharge experiment shows that the plasma jet generally presents three discharge modes, namely, filamentous argon discharge (P < 120 W), bright argon plasma filaments covered by Ar/Zn thin plasma layers (120 W ≤ P ≤ 150 W), and bright thick Ar/Zn plasma columns (P ≥ 155 W). The optical emission spectrum indicates that the electron temperature is ∼4000–5000 K, the electron density is on the order of 1015 cm−3, and the plasma has the characteristic of local thermodynamic equilibrium. According to the transient discharge photos and the simulated electric fields, the mechanism of the three discharge modes and their transformations could be attributed to the combined interactions (the mutual resonance enhancement between the surface wave and the plasma jet, the propagation of the ionization wave, and the different particle states in the Ar/Zn pulsed microwave plasma). The results have suggested that the large-scale Ar/Zn pulsed microwave plasma jet can be generated by adding Zn vapor into the Ar microwave plasma jet and the proposed Ar/Zn pulsed microwave plasma jet is suitable for the application of plasma ignition and combustion.