Spectroscopic Measurements of Parameters in a Low-Density Alkali-Metal Plasma

Abstract

The different parameters (temperature and density) of an alkaline plasma can be obtained by spectroscopic study provided that the plasma is of sufficiently high density. However if the electron density is lower than 1013 cm−3, the usual methods can no longer be directly applied. The aim of this study is to consider methods which hold good for low densities and to deduce the parameters and properties of a hot-cathode-discharge cesium plasma. The optical study of the cesium emission spectrum is limited to high excited levels for which partial local thermodynamic equilibrium is achieved and enables us to determine the gas temperature. We conclude that the population of high excited levels (greater than 10S, 9P, and 7F) of the cesium atoms is determined by collision processes among heavy particles. Electron density is measured from stark profiles of lines corresponding to the fundamental series 5D-nF with 14≤n≤17. This method allows density determination between 1012 and 1013 cm−3, i.e., for a region where spectroscopic density measurements are not usually possible.