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Jiang, Ke (2011): Particle manipulation in plasma device & Dynamics of binary complex plasma. Dissertation, LMU München: Fakultät für Physik



A complex plasma is a suspension of nano- to micron-sized dust particles immersed in a plasma with ions, electrons and neutral gas molecules. Dust particles acquire a few thousands of electron charges by absorbing the surrounding electrons and ions, and consequently interact with each other via a dynamically-screened Coulomb potential. Dust particles in a complex plasma can be controlled through a low frequency electrostatic distortion. We studied the transport velocity of the particles as we modulate the frequency and phase of the applied voltage by a segmented electrode. We used molecular dynamics to simulate our experimental observations, using plasma conditions from independent particle-in-cell simulations. We found that the transport of dust particles controlled by low-frequency modulation in our simulations are in good agreement with our experimental findings. This work is in the aim of, on one hand, providing a potential technique for addressing the dust contamination issues in plasma processing reactors and on the other hand, providing a setup for investigating large two-dimensional complex plasma systems where boundary effects can be avoided. We then proceeded to study the non-additivity effect in a complex plasma containing two different sizes of dust particles (binary complex plasma). For dust particles of type 1 and 2, the 1-2 (inter-species) interaction is always more repulsive than the geometric mean of 1-1 and 2-2 interactions. This asymmetry in the mutual interaction is called positive non-additivity. We used Langevin dynamics simulations for the Yukawa interacting particles characterized by positive non-additivity. We found that the two types of particles can separate into fluid-fluid phases and the growth of characteristic domain length follows a simple power law with an exponent of about 1/3 until the coupling strength is small enough, which is in a good agreement with the Lifshitz-Slyozov growth law for the initial diffusive regime of phase separation. We then used Langevin dynamics simulations to probe the influence of non-additive interactions on lane formation. We revealed a crossover from normal laning mode to a demixing dominated laning mode. In addition, we found that the lane formation is strongly influenced by the exact spatial configurations at the very moment of contact between two different complex plasmas. We also used hydrodynamics to model the evolution of Mach cones in complex plasmas. The hydrodynamic model was able to reproduce a compressional-wave Mach cone observed onboard the International Space Station.