Characterization of Kilohertz-Ignited Nonthermal He and He/ Plasma Pencil for Biomedical Applications

In this paper, an atmospheric pressure low-temperature plasma pencil generated in helium and helium/ oxygen gas mixtures was characterized in detail for its discharge characteristics, plasma power, reactive plasma species produced, plasma density, and plasma temperatures using electrical and optical emission spectroscopy (OES) diagnostics, and its efficacy for biomedical application. A visible plasma plume length of approximately 27 mm was generated using a 60-kHz ac HV power supply. The OES results showed the most intensive plasma emission lines of OH transition A²Σ⁺(v = 0, 1)→X²Π(Δν = 0) at 308 nm and OH transition A²Σ⁺(v = 0, 1)→X²Π(Δν = 1) at 287 nm, O I transition 3p⁵P→3s⁵S⁰ at 777.41 nm, O I transition 3p³P→3s³S⁰ at 844.6 nm, and N₂(C-B) second positive system with electronic transition C³ Π_u→B³Π_g in the range 300-450 nm. The effects of controlled oxygen content on the plasma pencil and on various helium plasma emissions and electrical properties are studied. A spatial distribution of reactive plasma species produced by the plasma pencil is presented. The electron density of plasma jet was estimated to be in the order of 2.1 × 10¹⁴ cm^-3 using Stark broadening line profile of the hydrogen alpha emission. The temperatures of afterglow plasma pencil were evaluated using OH rotational temperatures, and the results demonstrate temperatures of 316 and 362 K for pure He and He/O₂ gas mixtures (0.1% O₂), respectively. Preliminary results on inactivation of Streptococcus pneumoniae on a solid surface and in liquid suspension were carried out using the plasma pencil for biomedical applications.