Electrical and Spectral Characteristics of a Low-Temperature Argon–Oxygen Plasma Jet With Syringe Needle-Ring Electrodes

Abstract

Low-temperature atmospheric-pressure argon–oxygen plasma jet is generated with syringe needle-ring electrodes, which is powered by a sinusoidal excitation voltage at 8 kHz. The volume percentage of the oxygen content in the argon gas is as high as 12.5%. It is found that the rotational temperature of nitrogen is in the range of 297–320 K, and the vibrational temperature is almost unchanged to be about 2475 K, which is obtained by comparing the simulated spectrum with the measured spectrum at the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$C^{3} \Pi_{u} \rightarrow B^{3}\Pi_{g}\ (\Delta v = -2)$</tex></formula> band transition. The electronic excitation temperature is in the range of 8587–8994 K as obtained by the Boltzmann's plot method, the electron temperature at the tip of syringe needle is about 7.3 eV as estimated by the Einstein's equation, and the densities of atomic oxygen and molecular nitrogen are, respectively, on the order of magnitude of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$10^{16}\ \hbox{cm}^{-3}$</tex></formula> as determined by actinometry method, respectively. Moreover, the 2-D and 1-D distributions of the electric field magnitude are estimated by the 2-D finite-element software. At a time of 45.7 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{s}$</tex></formula> and an instantaneous applied voltage of 8 kV, the electric field magnitude at the edge of the ring ground electrode is the largest, and it is 15.9 kV/cm at the tip of the syringe needle.