Particulate imaging diagnostics in a gas-discharge plasma

A method of detecting particulates in gas-discharge plasmas is video microscopy with laser illumination. A standard approach in analyzing the video images is the moment-method of measuring the positions of particulates, which makes it possible to measure their concentrations. To also measure their velocities, as a new development in this diagnostic, we employ the Crocker-Weeks\footnote{ J. Crocker and D. Grier \textbf{J. Colloid. Interf. Sci.} 179, 298} algorithm to track particles. We demonstrate this diagnostic method in a capacitively coupled RF argon plasma, under challenging conditions when a cloud of particulates is accelerated to high velocities by the electrical sheath around a moving wire. The micron-sized particulates were electrically levitated in the sheath above the lower electrode in the plasma chamber.