The Structure of Self-Excited Dust-Density Waves Under Microgravity

Dusty plasmas under microgravity conditions are a great opportunity to observe dynamical processes in strongly coupled systems. For example, in such systems, self-excited dust-density waves can occur at low gas pressures in extended regions of the discharge. Recently, we have performed a series of measurements in a parallel-plate RF reactor during parabolic flights. It reveals that the waves can appear in two completely different states. One of them yields a high spatial and temporal coherence of the density fluctuations. This feature allows us to utilize scanning video microscopy to obtain information on the structure of the 3-D wave field. Under different experimental conditions, we also found that a wave field with multiple different wavelengths can arise in the dust volume. This results in defects in the wave pattern due to merging wavefronts. We determine their temporal evolution, which can be derived accurately from the phase information.