Electron density characterization of 27.1 and 50 MHz inductively coupled plasmas by means of Abel corrected Stark broadened H β line profiles

Abstract

Stark broadened profiles of the H β line were employed to obtain spatially resolved electron number densities in 27.12 and 50 MHz inductively coupled plasmas emission sources. A computerized system was developed for measuring the H β line profile with two stepping motors, which together provided a wavelength scan of the H β line profile, as well as a lateral displacement of the plasma image across the entrance slit. This system thus enables the spatially integrated Stark broadened H β line profile radiances to be converted to radially corrected profiles by using Abel integral equations. The fractional Stark widths (α 1 2 ) calculated by Griem were used to obtain electron density values from the halfwidths of the radially resolved H β line profile. Electron number densities were obtained at various heights and gas flows to characterize the electron number density gradients, which ranged between 1 × 10 21 and 5 × 10 21 m −3 for these investigations and agree very well with values obtained by methods based on continuum measurements and the Saha-Eggert equation.