Inferring plasma parameters from the sheath characteristics of a dc biased hairpin probe

Abstract

In this paper, the cylindrical sheath around a hairpin resonator probe has been varied by applying a dc potential to the hairpin to infer different plasma parameters in an argon and oxygen discharge. As the sheath width increases due to negative bias, the resonance frequency of the hairpin correspondingly shifts toward a lower value. An analytical model based on fluid approximation has been developed to estimate the sheath width variation as a function of the applied voltage on the probe. The analytical result is then compared with the well-known capacitance model that assumes a conjugate dielectric region around the hairpin consisting of a pair of cylindrical sheaths and the plasma. Using this method, a wide range of plasma parameters, including the electron temperature plasma potential and electronegativity parameter , have been obtained in an electronegative oxygen discharge. The advantage of this method over the conventional floating hairpin resonator probe has been qualitatively discussed.