Imaging of the Dust Acoustic Wave to Explore Synchronization

A self-excited dust acoustic wave is synchronized by sinusoidal modulation of the ion density, and the wave is imaged by planar laser-light scattering. Space-time diagrams based on the images reveal how the nonlinearity of the plasma’s response causes the wave’s frequency to be synchronized to a multiple of 0.5, 1, 2, or 3 of the modulation frequency. Space-time diagrams also reveal wave front merging as is observed for a wide range of modulation frequencies.