This cumulative dissertation discusses the experimental observation and description of crystallization and demixing processes in a three-dimensional complex plasma. Complex plasmas are low temperature plasmas to which well-defined microparticles have been added deliberately. These particles are charged by electron and ion fluxes toward their surfaces. Charged particles can then create regular structures similar to a crystal or arrange comparable to fluids. The typical size and time ranges in a complex plasma allow for observations of changes in form of distinct phases on a single-particle level. This is why they are often used as model systems for phase transitions.In the first publication, the influence of neutral gas pressure on the crystallization of a three-dimensional complex plasma under gravity conditions was considered. The ´scalar product of the Minkowski structure metric´ was developed in this publication to identify the particles´ state of aggregation. Besides this method, various well-known crystallization criteria were applied. All criteria revealed the same picture: the system was in the crystalline state at low pressure and in the liquid state at high pressure. This stands in contrast with previous experiments under gravity as well as under microgravity conditions. The increasing role of collisions between ions and neutrals in the vicinity of the particles as well as a decreased Debye length were identified as responsible for this observation.The second publication is a logical extension of the first one. In this publication, the scalar product of the Minkowski structure metric was applied to visualize the location of the particles in the solid state and in the liquid state at different pressure rates. Hereby, it could be shown additionally that the degree of crystallization was decreasing from the lower to the upper part of the particle cloud.After the first two publications, the detailed conditions under which complex plasmas are highly ordered were determined. This knowledge facilitated the third publication. In this publication, the crystallization process of a complex plasma under gravity conditions was analyzed in a time-resolved manner. During crystallization, tomographic scans were performed to identify the evolution of solid clusters. The calculated fractal dimension of these clusters showed that the solidification process was dominated by epitaxial growth and diffusion-limited growth.The fourth publication deals with the demixing of two particle types in a complex plasma. Due to the mass discrepancies, the particles would levitate at different heights in the plasma under gravity conditions. This is why the experiments were performed under milligravity during a parabola flight. The transition from a single phase into a two-phase system was observed and described.
Verknüpfung zu Publikationen oder weiteren Datensätzen
