Dynamics of charged dust grains in RF plasma sheaths.
CM Ticos
Los Alamos National Laboratory,
Micron-size dust grains acquire a negative charge when introduced into a low
pressure RF plasma and levitate in the sheath of the lower RF driven electrode
due to a balance between the upward electrostatic force and the downward forces
of ion drag and gravity.
The equilibrium state of dust grains is sensitive to changes in the sheath
potential distribution or neutral gas pressure. It is showed that a DC negative
bias applied to the RF driven electrode causes the lowest grains of a dust
cloud to fall through the sheath, to the driven electrode. Analysis of the
grain falling trajectories can provide information about the local sheath
electric field.
Waves with constant frequency are observed to propagate in a dust cloud as the
neutral gas pressure is reduced below a critical value. The ion-dust streaming
instability is thought to be the mechanism responsible for the excitation of
the observed dust waves.