Sheath-to-sheath transport of dust particles in a capacitively coupled discharge

Abstract

Transport of micrometer-sized dust particles in a capacitively coupled radio frequency discharge at low pressures of a few Pa is realized experimentally and understood by a kinetic particle simulation combined with a model. Applying a voltage waveform, which consists of two consecutive harmonics with a variable phase angle, θ, to one electrode, control of both the spatial potential profile and the ion density distribution is obtained by adjusting θ. In this way, the electrostatic and ion drag forces, on dust particles initially located at the sheath edge adjacent to the lower electrode, are controlled. The sudden change of θ leads to an abrupt change of the sheath width. This introduces the particles instantaneously into a high potential that accelerates them to high kinetic energies. The experimental results show that a certain minimum change of the discharge symmetry, i.e. of the phase angle, is required to allow the transport of dust particles through the plasma bulk. Beyond this threshold, a part of the transported particles can even be trapped around the edge of the opposing (upper) sheath.