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Theoretical and experimental studies of low-frequency electrostatic waves in plasmas containing negatively charged dust grains are described. The presence of charged dust is shown to modify the properties of ion-acoustic waves and electrostatic ion-cyclotron waves through the quasineutrality condition even though the dust grains do not participate in the wave dynamics. If the dust dynamics is included in the analysis, new ''dust modes'' appear-dust acoustic and dust cyclotron modes. The results of laboratory experiments dealing with dust ion acoustic ͑DIA͒ waves and electrostatic dust ion cyclotron ͑EDIC͒ waves are shown. These modes are more easily excited in a plasma containing negatively charged dust. Finally, observations of dust acoustic ͑DA͒ waves are presented and measurements of the dispersion relation are compared with one obtained from fluid theory.

Dust particles emerged in plasma acquire electric charges collecting elec trons and ions, by photo-emissions, secondary electron emission, thermoionic emission etc. The study of the charge fluctuation problem of dusty plasma is important for the interpretation o f various astrophysical and laboratory phe nomena. Charge fluctuation plays an important role in dusty plasma. It leads to damping of the dust-acoustic mode, unstable high frequency plasma modes and negative energy mode for streaming ions in the background o f fixed dust.

An experimental investigation of dust acoustic ͑DA͒ waves in a dc glow discharge plasma is described. The glow discharge is formed between a 3 cm anode disk and the grounded walls of a 60 cm diameter vacuum chamber which is filled with nitrogen gas at a pressure of about 100 mTorr. Dust located on a tray in the chamber is attracted into the plasma where it is trapped electrostatically. The dust acoustic waves were produced by applying a modulation signal ͑5-40 Hz͒ to the anode. The wavelength of the DA waves was measured from single frame video images of scattered light from the dust grains. The measured dispersion relation is compared with theoretical predictions.