4 WAYS TO DETERMINE THE ELECTRON-DENSITY IN LOW-TEMPERATURE PLASMAS

Four ways to measure the electron density in low-temperature plasmas a re presented: Thomson scattering, Langmuir probe, optical-emission spe ctroscopy, and continuum-radiation analysis. The results of the four m ethods are compared to each other and discussed. For the electron-dens ity range of 10(19)-10(21) m-3, Thomson scattering proved to give the most accurate results (within a few percent); the Langmuir-probe measu rements also proved acceptable (25%). A collisional-radiative-model fi t through excited-level populations and continuum analysis yields resu lts in good agreement with Thomson scattering data, although with larg er margins of error (around 40%). A simple Saha fit proved to be inade quate.