Reports on a simple experimental technique which can be used for determination of the plasma where the plasma potential prevails; these ions are accepted by the analyser plate when phi c= phi pl. Part of this technique has been used by Andersen, Jensen, Michelsen and Nielsen (1971) in measurements of the ion velocity distribution function in a Q-device. It is suggested that this technique might be useful in satellite measurements of the ion energy distribution function in the solar wind.
Andersen, S. A., Christoffersen, G. B., Jensen, V. O., & Michelsen, P. (1972). Methods for direct measurement of the plasma potential. Plasma Physics and Controlled Fusion, 14(2), 202-204. https://doi.org/10.1088/0032-1028/14/2/011