Complex plasmas: Interaction potentials and non-Hamiltonian dynamics

This thesis is a cumulative dissertation that consists of three
papers. The first paper addresses the issue of screening of a
charged dust particle suspended in the plasma-wall transition layer
of a plasma discharge. This problem is one of the fundamental
issues in the physics of complex (dusty) plasmas, because the
screening of charged dust particles determines the interaction
forces between them and thus governs their dynamics. The kinetic
model proposed in this paper considers a point charge embedded in a
weakly-ionized plasma with ion drift. The latter is considered to
be due to an external electric field and assumed to be
mobility-limited. Here, "mobility-limited" means that the
acceleration of ions in the external field is balanced by
collisions of ions with neutrals and that this balance determines
the drift velocity. The embedded point charge (i.e., a charged dust
particle) perturbs the ion drift, and the resulting potential
distribution around the dust particle is calculated. The results
are proven to be in agreement with existing measurements performed
in the plasma-wall transition layer of a rf plasma discharge. One
of the important applications of this work is related to the
possibility of tuning the pair interaction potential between dust
particles by applying an external oscillating electric field. In
particular, such a tuning allows studying electrorheological
properties of strongly coupled systems on all relevant time scales.
First experiments of this kind have already been performed onboard
the International Space Station. The second paper deals with the
dust-lattice waves - oscillations of charged dust particles forming
a crystalline structure in a plasma. The role of anisotropic
screening of dust particles and variations of their charges is
investigated. It is well known that the mentioned effects lead to
non-Hamiltonian dynamics of dust particles and, as a result, can
trigger an instability of the dust-lattice waves. This instability
has been already observed in experiments. The new result is that
the mutual influence of particles on their charges, not considered
in the analysis of the dust-lattice waves before, is shown to be
capable of making a significant contribution to this instability.
The third paper examines whether a similar instability can be
observed in a cluster formed by two or three charged dust
particles. It is found that an instability due to the
non-Hamiltonian dynamics is only possible when the interparticle
separation in the cluster is such that certain cluster
eigenfrequencies are sufficiently close to each other.