Spectroscopic investigation of a lanthanide iodide/mercury arc discharge plasma

Abstract

An investigation was made of the distribution of Dy atoms and ions and iodine atoms in the central region (r/R≲0.6) of a DyI₃/Hg‐arc plasma. The arc is operated horizontally; it is centered magnetically. The mercury pressure is 4.5×10⁵ N m⁻², the input power 500 W, the electrode distance 37 mm, and the tube diameter is 15 mm. The temperature profile was determined from the emission of the optically thin Hg 577.0‐nm line. The side‐on emission distributions of optically thin Dy⁺ and Dy lines, in combination with the optical absorption of Dy⁺ resonance lines, indicate a radial depletion of dysprosium at the arc center, which can be explained by a simple model. Combination of experiments and calculations in which ambipolar diffusion is taken into account yields the distribution of Dy atoms and ions in the central region. The distribution of the iodine atoms was determined from the emission of the optically thin I 905.8‐nm line. The iodine content of the arc exceeds the dysprosium content by about an order of magnitude. The chemical composition of the arc plasma is discussed. Measurements and calculations on self‐reversed Dy lines also show that ambipolar diffusion is a dominant process.