The inflection point technique in the limit of zero emission determines the plasma potential by fitting a straight line to the graph of the emission current versus the inflection point of the emissive probe I-V traces. The plasma potential is determined by extrapolating the line to the limit of zero emission. The effects of wire thickness, gas composition, neutral pressure and position on the technique were investigated. Experiments were performed in a multi-dipole filament discharge. Wire thicknesses of 0.013, 0.025, 0.05 and 0.1mm were studied. Experiments were done in Argon, Xenon and Helium plasmas with neutral pressures ranging from 0.5mTorr to 3mTorr. Measurements were performed from the bulk of the plasma to its sheath edge near a 10cm diameter negatively biased plate.

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This work is supported by U.S. DOE under the Grant and Contract Nos. DE-FG02-97ER54437 and No. DE FG02- 03ER54728, DE SC0001939 and by the National Science Foundation Grants under the Grant and Contract Nos. CBET-0903832, and No. CBET-0903783.