  Dust particles often form vertical chains due to the influence of the
wakefield produced by the streaming ions in the plasma sheath. These particle
chains are proving useful as a unique diagnostic tool for investigating the
physics behind the basic properties of the ion wakefield within the plasma
sheath. In this paper, an experimental method is presented for investigating
the ion wakefield which employs a new oscillation technique designed to perturb
a two-particle vertical chain. Using this technique, damped free fall
oscillations are generated via an external DC bias to the lower electrode. A
fast Fourier transformation is then used to produce a spectrum from the
collected oscillation data and a center of mass oscillation is identified.

Plasma Physics