A COMPARISON OF METHODS OF DETERMINING ELECTRON DENSITIES IN AFTERGLOW PLASMAS FROM LANGMUIR PROBE CHARACTERISTICS

A diversity of opinion exists at the present time concerning the interpretation of single Langmuir probe characteristics, in particular with respect to the location of space potential and the determination of charged particle number densities from the characteristics. This work describes measurements made with very small Langmuir probes in gaseous afterglow plasmas at room temperature where conditions for a study of this kind are expected to offer particular advantages. A comparison is made of the values of electron densities obtained from the characteristics using six methods which are commonly used. Good agreement is found to exist between those deduced from the orbital limited characteristics in the accelerating region for electrons and those calculated from the probe current at the inflexion point of the characteristics. That these are also in tolerable agreement with those obtained using the intersecting tangents method is thought to be fortuitous.