Optical emission spectroscopy diagnostics of an atmospheric pressure direct current microplasma jet

This paper is about the use of optical emission spectroscopy as a diagnostic tool to determine the gas discharge parameters of a direct current (98% Ar–2% H2) non-thermal microplasma jet, operated at atmospheric pressure. The electrical and optical behaviors were studied to characterize this glow discharge. The microplasma jet was investigated in the normal and abnormal glow regimes, for current ranging from 10 to 130 mA, at ~ 220 V of applied voltage for copper cathode. OH (A 2∑+, ν = 0 → X 2Π, ν′ = 0) rotational bands at 306.357 nm and also the 603.213 nm Ar I line, which is sensitive to van der Waals broadening, were used to determine the gas temperature, which ranges from 550 to 800 K. The electron number densities, ranging from 6.0 × 1014 to 1.4 × 1015 cm− 3, were determined through a careful analysis of the main broadening mechanisms of the Hβ line. From both 603.213 nm and 565.070 nm Ar I line broadenings, it was possible to obtain simultaneously electron number density and temperature (~ 8000 K). Excitation temperatures were also measured from two methods: from two Cu I lines and from Boltzmann-plot of 4p–4s and 5p–4s Ar I transitions. By employing Hα line, the hydrogen atoms' H temperature was estimated (~ 18,000 K) and found to be surprisingly hotter than the excitation temperature.