Complex plasmas: Interaction potentials and non-Hamiltonian dynamics
This thesis is a cumulative dissertation that consists of three papers.\n\nThe 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.\n\nThe 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.\n\nThe 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.