Spatially-resolved observation of the excitation temperature in a glow discharge plasma for atomic emission spectrometry

A two-dimensionally imaging spectrometer system was employed to obtain the spatial distribution of the excitation temperature in a glow discharge plasma for emission analysis. A Grimm-style glow discharge excitation source, whose hollow anode had an inner diameter of 8 mm, was observed over the whole emission area. The mapping of the excitation temperature was conducted by using a two-line method under the assumption of the Boltzmann distribution. Iron was chosen as the probe element, and a pair of the atomic lines: Fe I 371.99 nm (3.33 eV) and Fe I 375.82 nm (4.25 eV), were employed for the measurement. The excitation temperature was a little varied over the plasma region except for the edge portion, even when the discharge voltage as well as the argon pressure were changed as the experimental parameters. The temperature was estimated to be 4650 - 4950 K at a central portion of the plasma having a 5-mm-diameter circle, implying that the emission excitation at the central portion occurred almost uniformly for each discharge condition.