Estimation of the air impurity level inside the dielectric barrier discharge (DBD) device and effect of air impurity in the plasma chemistry

A substantial device size is required to utilize the dielectric barrier device in food processing at atmospheric pressure. The understanding of air impurities present in the device is of utmost significance, as it significantly changes plasma chemistry. Increasing feed gas flow rate (GFR) from 1.5 to 5 slm changes the air impurity within the discharge device from 1180 to 265 ppm. This change is assessed using a new technique reliant on time-dependent optical emission spectroscopy (OES). The effective lifetime of metastable helium increases with GFR. The density of excited plasma species [O2+, N2+, N4+, O4+, N2+(B), N2(C)] is predicted considering 82 reactions among electrons, He, N2, and O2 for different air impurity levels. This paper compares the excited plasma species identified in our investigation with those documented in different published literature. It has been shown that termolecular reactions affect the density of O4+ and O2+. It also confirms that instead of the O4+ ion formation reaction, the O2+·N2 cluster ion formation reactions are the dominant reaction mechanism in that experimentally relevant air impurity level within the discharge zone. It also shows that at low impurity levels (1–30 ppm), medium impurity levels (30–250 ppm), and at the air impurity ranges from 250 to 1000 ppm, N2+ (∼1012), N4+ (∼1011), and O2+ ·N2 (∼1011 cm−3) cluster ions are the dominant ionic species, respectively. The OES reveals that there is a prominent emission from O2+ at higher GFR, which plays an important role in the chemical reaction.