Surface contamination of active electrodes in plasmas: Distortion of conventional Langmuir probe measurements

Abstract

Laboratory experiments were conducted to determine the effectiveness of a newly developed pulse technique in eliminating surface contamination effects and associated hysteresis in Langmuir probe current‐voltage characteristics. We found that (i) the pulse technique was superior to the conventional continuous sweep approach to Langmuir probe diagnostics; (ii) substantial potentials can develop across contaminating surface layers and that these potentials can vary in the conventional Langmuir procedure resulting in determinations of electron energies higher than actually present in the ambient plasma; and (iii) attempts to achieve ’’clean‐probe’’ operation by heating can be of limited value.