Improved inflection point method of emissive probe for accurate measurement of plasma potential

The potential of the inflection point of emissive probe characteristics ( V i p ) in the limit of zero emission is considered to be an accurate indication of the plasma potential. Previous method for this limit is linearly extrapolating the change of V i p with respect to the electron emission current I e m i s to the limit I e m i s ≈ 0 , which may result in inaccurate results since evidences showed that V i p does not change well linearly with I e m i s . The authors found in this study that, instead of I e m i s , V i p changes linearly with the probe heating current ( I h t ) which is a function of the probe temperature ( T p ), and the phenomenon is reasonably interpreted by the space charge voltage increasing linearly with T p . An improved inflection point method of emissive probe, which utilizes linear extrapolating the V i p − I h t relation to the heating current for initial emission, is proposed for accurate measurement of plasma potential.