Probe Contamination in a Hydrogen Plasma†

Abstract

By making use of operational differentiation, the method of time differentiation has been applied successfully to obtain second derivatives of Langmuir probe i-V characteristics in a hydrogen plasma. It is demonstrated that under certain conditions contamination of the probe by cathode material may result in an additional peak in the electron energy distribution. This is most pronounced when a well-defined group of fast electrons (>6ev) is present and may be attributed to the ionization of barium in the vicinity of the probe surface.