Externally and self-excited nonlinear waves in a dusty plasma.

Recently it has been shown that strongly coupled three-dimensional dust clouds can be easily levitated in the plasma sheath region of a glass box coated with a transparent yet conductive layer of indium tin oxide (ITO). Gradually reducing the neutral gas pressure below a critical value of $\sim $350 mTorr establishes self-excited waves within this system. In this paper, it will be shown that decreasing the ITO bias to $-$20 V allows waves to be externally induced within the lower region of the dust cloud. The underlying physics and synergistic effect of changing the pressure and/or ITO bias on these waves will be examined as will the onset of instabilities and the evolution of the dust density waves for ITO biases ranging from 0 to $-$40 V. Finally, the dust charge will be estimated by assuming the waves oscillate at the dust plasma frequency.