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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 A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=0) at 308 nm and OH transition A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=1) at 287 nm, O I transition 3p^5P\to 3s^5S^0 at 777.41 nm, O I transition 3p^3P\to 3s^3S^0 at 844.6 nm, and N2(C\-B) second positive system with electronic transition C^3\Piu{\to}B^3\Pig 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\times 10^14~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. [ABSTRACT FROM PUBLISHER]

An atmospheric pressure needle plasma is generated with a hollowneedle-plate dielectric barrier discharge, and the plasma parameters are measured by optical emission spectroscopy. The length of the needle plasma reaches 3 cm with an argon flow rate in the range from 3.5 to 6.1 ml/min when the applied voltage is 7.2 kV. The spatial distribution of oxygen-atom spectral-line intensity indicates that there is a large concentration of excited oxygen atoms in the middle of the plasma. Gas temperature is estimated by simulating the spectrum of OH radical around 309 nm. The spatial distribution of gas temperature along the plasma is uniform. Gas temperature decreases with the increase in argon flow rate. Electron density determined by the Stark broadening of H\alpha is in the range from 5.8 \times 10^14 to 6.0 \times 10^14\ \cm^-3 when the electron temperature is 1–4 eV. The application of plasma in the modification of material surface is demonstrated. [ABSTRACT FROM PUBLISHER]