A Comparative Study of Electron Density Determination Methodologies in the Helium Microwave-Induced Plasma

Abstract

Electron number densities were examined in a low-power atmospheric-pressure helium microwave-induced plasma. Two hydrogen-based methods and two helium-based methods were employed to estimate electron concentration. The hydrogen 4471 Å Balmer line was examined with the use of both line shape and full width at half-maximum intensity measurements. The data suggest that half-width calculations underestimate electron densities. Half-width measurements of neutral helium lines result in number densities which appear to be overestimated. This inaccuracy is thought to be the result of apparatus broadening. Finally, the use of quasi-degenerate helium neutral lines possessing forbidden and allowed components afforded electron concentrations similar to those derived from the Balmer beta line shape analysis.