Tomographically resolved ionization temperatures and electron densities in the inductively coupled plasma determined by the line-to-continuum method

Abstract

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by three disks with data files with the hardcopy paper in Word 5.0 and ASCII format, and a disclaimer. The text details the purpose of the work and the structure of the three-dimensional Ar ionization temperature and electron number density data files. The line-to-continuum method was used to evaluate the spatial distribution of Ar ionization temperatures, T ion, and electron number densities, n e, within a dry Ar inductively coupled plasma (ICP). The emission measurements were spatially resolved in three dimensions by reconstruction algorithms for computed tomography. The 40.68 MHz Ar ICP was operated at applied r.f. power levels of 0.75 and 1.0 kW. The reconstructed distributions of Ar I line emission (430.0 nm) and continuum emission (428.6 nm) show good reproducibility over a series of five replicate runs. Argon ionization temperatures remain within a 6500–8500 K range throughout the continuum-emission cone of the plasma. Deviations from this temperature range occur in the central channel and around the outer edge of the plasma. Low in the plasma, the central-channel T ion is cooler than 6000 K. Along the outer edge of the plasma, the line-to-continuum ratio becomes small; this low ratio results in erroneously high temperatures (> 12000 K). The errors in T ion appear to be due to reproducible artifacts in the reconstruction process that lead to low Ar I line-emission readings along the outer edge of the plasma. Electron densities show a maximum of 8.5 × 10 14 cm −3 and 1.2 × 10 15 cm −3 at 0.75 and 1.0 kW, respectively. Electron number densities were much better behaved than T ion due to their dependence on the square-root of continuum measurements and only the fourth-root of T ion.