Four ways to determine the electron density in low-temperature plasmas

Four ways to measure the electron density in low-temperature plasmas are presented: Thomson scattering, Langmuir probe, optical-emission spectroscopy, and continuum-radiation analysis. The results of the four methods are compared to each other and discussed. For the electron-density range of 10¹⁹--10²¹ m^-3, Thomson scattering proved to give the most accurate results (within a few percent); the Langmuir-probe measurements also proved acceptable (25%). A collisional-radiative-model fit through excited-level populations and continuum analysis yields results in good agreement with Thomson scattering data, although with larger margins of error (around 40%). A simple Saha fit proved to be inadequate.