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A.A. Sickafoose, J.E. Colwell, M. Horanyi, S. Roberston (University of Colorado, LASP)
Prime examples of active dust transport near surfaces in the solar system include dust grains suspended above the lunar surface, spokes observed in Saturn's rings, and recent images of infilled craters from the NEAR spacecraft at Eros. Dusty regoliths are produced by the interplanetary micrometeoroid flux on nearly all airless bodies in the solar system. Therefore, understanding dust charging, levitation, and dynamics above surfaces is important for interpreting remote sensing data and analyzing the evolution of most planetary surfaces. The interaction between charged dust particles and a photoelectron layer or plasma sheath above the surface is the most likely explanation for the observed dust dynamics.
We report the results of experiments on the levitation of dust particles in an Ar plasma sheath above a flat, conducting plate. Types of particles tested include hollow and solid glass microballoons (<45 microns in diameter), polystyrene DVB microbeads (5 microns and 10 microns in diameter), and JSC-1, a lunar regolith simulant (<25 microns in diameter). Plasma characteristics are determined using a Langmuir probe and an emissive probe measures sheath potential profiles. Dust particles levitating above the surface of the plate are illuminated by an Ar laser and observed by a video camera. Our experimental results suggest the following: (1) various types and sizes of particles can levitate in a plasma sheath above a plate; (2) particle dynamics in the plasma sheath above the plate can be quite complex; (3) particle levitation height and corresponding charge are comparable to the values calculated from orbital motion limited (OML) theory; (4) exposure to a UV source slightly alters the particle levitation height; (5) a mechanism to inject particles into the sheath is not necessary given a large enough plate bias.
This work is supported by NASA's Microgravity Fluid Physics Program and NASA's Office of Space Sciences GSRP.