A homogeneous atmospheric pressure air plasma in a 10 mm gap based on a three-electrode configuration

Generation of atmospheric pressure homogeneous air plasma in a large gap (> 4 mm) is a challenge. In this study, an atmospheric pressure homogeneous air plasma generated in a gap up to 10 mm is reported, which is based on a three-electrode configuration, where a high-voltage (HV) electrode and a middle electrode form a surface dielectric barrier discharge (S-DBD), and together with the ground electrode form the main volume discharge. High-speed photographs confirm that the discharge in the main gap is homogeneous. The gas temperature of the plasma estimated from the N₂(C³Π_u-B³Π_g) (Δv = −2) emission is about 320 K, which is close to room temperature. A detailed analysis shows that the discharge ignited between the HV electrode and the middle electrode is serving as an electron source, and the electrons deposited on the dielectric plate are due to the S-DBD along with the applied voltage generating a driving force, which results in a high concentration of seed electrons in the main gap and induces the homogeneous plasma. Further analysis shows that the electric field in the main gap is only about 18.45 kV·cm⁻¹, which is much lower than the typical breakdown electric field of 30 kV·cm⁻¹ for atmospheric pressure air discharge.