Comparative Studies of Atmospheric Pressure Plasma Characteristics Between He and Ar Working Gases for Sterilization

Helium (He) and Argon (Ar) atmospheric pressure plasma jets operated with low-frequency power source are designed and studied. The current and voltage waveforms, formation of plasma jets, estimated rotational and vibrational temperatures, optical emission spectra, and numerical simulations for He and Ar gases are investigated to analyze the plasma characteristics. Ar plasma shows higher discharge current and many instantaneous current peaks compared with He plasma. For gas flow between 1 and 7 L/min and applied voltage between 3 and 10 kV, no significant changes in Ar plasma are observed. He plasma is found to be sensitive as far as gas flow rate and applied voltage are concerned. This sensitivity is associated with a transition from laminar to turbulent mode of gas flow. The estimated gas temperatures show higher values for Ar plasma than those of He plasma. Ar plasma jet emits extremely high intensity of OH (305 nm ~312 nm) and O (777 nm) compared with that emitted from He plasma jet. High concentration of OH and O in Ar plasma is related with high density of electrons with 4-5 eV, which is in the range of the dissociation energy of H-H, O-H, and O=O bonds. As a result, wider sterilization area and higher sterilization efficacy in indirect treatment are observed for Ar plasma than He plasma.