Effects on non-Maxwellian electron energy distributions on the orbital limited current-voltage characteristics of cylindrical and spherical Langmuir probes under collisionless conditions

Abstract

The conventional method of measuring electron temperatures and densities from Langmuir probe data is based on the analysis of the electron retarding region characteristics. However, the errors associated with this method can be considerable and as an alternative it has been suggested that measurements of the electron density and temperature may be obtained from the electron accelerating region characteristics, this technique in principle being inherently more accurate. A unified theory for idealised spherical and cylindrical probes, operated under orbital limited conditions in the electron accelerating region, is presented which permits a detailed examination of the effects of non-Maxwellian electron energy distributions on the current-voltage characteristics of such probes. It is shown that the electron density values derived from the accelerating region of a cylindrical probe are virtually independent of the electron energy distribution for large probe voltages, while the electron 'temperature' values derived from the accelerating region of a spherical probe are only weakly dependent on the precise form of the electron energy distribution.