Transport of dust in low-pressure RF discharges

The behaviour of dust particles in a discharge is the result of the concerted action of the charging process and forces like gravity, the ion and neutral drag force, and the thermophoretic force. When the amount of dust is large, the plasma parameters differ from those of a dust free discharge and self-consistent modelling of the plasma-dust coupling is needed. We have developed such a model and successfully applied it to dusty argon radio-frequency discharges under micro-gravity conditions. Since the ion drag force plays a major role, the reactor geometry and the ion density profile are important. Therefore, the geometry and the shape of the powered parts (like rings) of the electrodes are tools that can be used to modify the shape of the dust cloud and of the dust free central part, the void, that is usually observed in microgravity experiments. Here, we will show applications of the model to asymmetric reactors, and reactors in which concentric ring electrodes are used to power the discharge. This shows a way to obtain larger crystalline regions.