LANGMUIR-PROBE CHARACTERISTIC IN THE PRESENCE OF DRIFTING ELECTRONS

The electron current to a negatively biased, cylindrical Langmuir prob e is computed for the case of drifting, Maxwellian electrons in a low- pressure discharge. The degree of drift is characterized by v(d)/v(th) , where v(d) and v(th) are the electron drift and thermal speeds, resp ectively. We find that the inflection point of the characteristic unde restimates the plasma potential, for v(d)/v(th) > 1.25. Further, for v (d)/v(th) greater than about 0.1, an analysis assuming stationary elec trons computes an erroneously high temperature. Probe data from a sput tering magnetron discharge are fitted with the drifting model, giving a concrete example of its use.