The interaction of stationary and moving objects with dusty plasmas

The interaction of an electrically floating metal object with a dusty plasma formed in a dc discharge was investigated experimentally. Three cases were studied in which (a) the object was at rest in the dusty plasma, or was moved through the dusty plasma with a speed that was either (b) on the order of the dust-acoustic speed or (c) much faster than the dust-acoustic speed. When the object was at rest, a dust-free cavity with a boundary with a sharp dust density gradient was formed around the object. The size of the cavity was largely determined by shielding of the object by the plasma ions. A similar (although dynamic) behavior was observed in the moderate speed case (case b). When the object was moved very rapidly (case c) the dust grains did not have time to respond, and the object mechanically removed the grains, leaving behind a narrow channel which quickly filled in.