Spatially resolved diagnostics of an atmospheric pressure direct current helium microplasma

Abstract

Optical emission spectroscopy measurements were performed with added trace probe gases in an atmospheric pressure direct current helium microplasma. Spatially resolved measurements (resolution ∼6 µm) were taken across a 200 µm slot-type discharge. Gas temperature profiles were determined from N2 emission rotational spectroscopy. Stark splitting of the hydrogen Balmer-β line was used to investigate the electric field distribution in the cathode sheath region. Electron densities were evaluated from the analysis of the spectral line broadening of Hβ emission. The gas temperature was between 350 and 550 K, peaking nearer the cathode and increasing with power. The electron density in the bulk plasma was in the range (4–7) × 1013 cm−3. The electric field peaked at the cathode (∼60 kV cm−1) and decayed to small values over a distance of ∼50 µm (sheath edge) from the cathode. These experimental data were generally in good agreement with a self-consistent one-dimensional model of the discharge.