We report a study of electron saturation current variations at varying probe heating that were found to be closely related to probe wire contamination. The study was performed in three types of low temperature argon plasma -the weakly magnetized plasma of a cylindrical magnetron, the non-magnetized plasma of a double plasma machine and a hollow cathode plasma jet, showing different trends. In the present work the effect of overestimation of the plasma potential by a strongly emitting probe is discussed and experimental data are compared with a theoretical model.

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We report on experimental investigations of the change of the electron saturation current of a dc-heated emissive probe with the probe heating current. According to the simple theory of the emissive probe, the electron saturation current should not be affected by emission. However, in many experiments a variation of the electron saturation current with the emission current was observed. We consider two possible reasons for such variations: (a) the influence of the space charge around the probe shaft, (b) the change of the work function of the probe surface material due to heating. We tried to find sufficient experimental evidence for supporting one or the other (or both) of these two explanations. We used two different types of plasma to validate the results: a cylindrical magnetron plasma and the non-magnetized plasma of a DP machine. From our experiments follows that the electron saturation current of the emissive probe is affected by the space charge effect as well as it depends on the probe wire material. : 52.25.Xz, 52.70.Ds PACS

Two similar experimental set-ups were used to measure axial and radial distribution of discharge plasma parameters at different magnetic fields. Both systems were cylindrical magnetrons with outer cylindrically-shaped anode and coaxially placed cathode -both the discharge vessels had diameters approximately 6 cm and they were 30 cm and 11 cm long respectively. In the longer magnetron the measurements were made using three radially movable cylindrical Langmuir probes placed at three different axial positions and in the shorter magnetron the axially movable probe was used. From the measurements there were evaluated electron density, electron mean energy, plasma potential and floating potential.