Synchronization of dust density waves in anodic plasmas

Abstract

Dust clouds can be confined in anodic plasmas by an equilibrium of the electric field force and the ion drag force. In these dust clouds self-excited dust density waves are observed as soon as the cloud length exceeds typical wavelengths. By superimposing an external modulation signal on the anode bias, the self-excited wave can be synchronized at the modulation frequency when the frequency is close to the natural frequency of the self-excited wave. For very low frequencies, an interaction of the center of mass motion of the cloud with the self-excited wave is found. For intermediate frequencies, close to the natural frequency of the self-excited modes, entrainment is observed, and for slightly higher frequencies a spatial cascade to subharmonic modes is found. At the highest frequencies, an influence of the modulation is still present, the wave is entrained if the modulation frequency is close to a rational factor of the natural frequency, as can be seen by the narrowing of the spectral components.