Laboratory Studies of Waves and Instabilities in Dusty Plasmas

Physics – Plasma Physics

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Scientific paper

Plasmas containing dust grains are found in many geophysical and astrophysical environments such as planetary rings, comet tails, noctilucent clouds, and the interstellar medium. `Dusty plasmas' are also present in devices used for plasma processing of semiconductors, in the exhaust of rocket engines, and in fusion devices. In typical laboratory experiments a micron-sized dust grain, having a mass of about a trillion times that of a positive ion, will acquire a negative charge corresponding to a few thousand electrons. The presence of this massive and highly charged species alters the conventional quasineutrality condition in an electron-ion plasma, modifying both the propagation characteristics and instability thresholds of the usual plasma wave modes. It also gives rise to new very low frequency `dust modes,' directly associated with the dust grain dynamics.(N. N. Rao, P. K. Shukla, and M. Y. Yu, Planet. Space Sci. 38), 543 (1990).^,(N. D'Angelo, Planet. Space Sci. 38), 1143 (1990). In this tutorial talk, I will first discuss some of the basic physics of waves in dusty plasmas followed by a presentation of our laboratory investigations of the effect of negatively charged dust on ion-acoustic waves(A. Barkan, N. D'Angelo, and R. L. Merlino, Planet. Space Sci. 44), 239 (1996). and current-driven electrostatic ion-cyclotron waves.(A. Barkan, N. D'Angelo, and R. L. Merlino Planet. Space Sci. 43) 905 (1995). These experiments were performed in a single-ended Q-machine which incorporates a rotating dust dispersal system(W. Xu, B. Song, R. L. Merlino, and N. D'Angelo, Rev. Sci. Instrum. 63), 5266 (1992). for introducing dust into the plasma. I will then describe our observations of `dust acoustic' waves performed in a DC glow discharge in which negatively charged dust grains are electrostatically confined.(C. Thompson, A. Barkan, N. D'Angelo, and R. L. Merlino, Phys. Plasmas 4), 2331 (1997). Dust-acoustic waves are low-frequency ion-acoustic waves (tens of Hz) in which the inertia is provided by the heavy negatively charged dust grains and the tension is provided by the ion and electron pressures. These waves are visually observable in the light scattered by the dust. A video recording of these waves will be shown as well as measurements of the dispersion relation.

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