Measurement of the electric charge on particulates forming Coulomb crystals in the sheath of a radiofrequency plasma

TLDR

Monodisperse electrically charged particulates (9.4 µm diameter) are trapped in the sheath of an argon RF parallel‑plate discharge, forming Coulomb crystals with horizontal hexagonal layers. A method for determining the particle charge is demonstrated by measuring the response to a modulation of the electrode bias. The approach uses electrode bias modulation to compare the strong‑coupling system to a one‑component plasma model and to a Yukawa potential model. Charges of about three to five thousand elementary units are measured, and the orbital‑motion‑limited (OML) charging model predicts higher charges than observed.

Abstract

Monodisperse electrically charged particulates (9.4 mu m diameter) are trapped in the sheath of an argon RF parallel plate discharge. The particulates form Coulomb crystals consisting of horizontal hexagonal layers. A method for the determination of the charge on the particles is demonstrated that uses the response to a modulation of the electrode bias. Charges about three to five thousand elementary units are measured. The commonly applied orbital motion limited (OML) charging model leads to charges higher than the measured values. The strong coupling system is compared to the one component plasma (OCP model) and to a model with Yukawa potentials.