Interaction between a dust cloud and a magnetized plasma in relative motion

The interaction between a dust cloud and a magnetized plasma is investigate d by use of an idealized model where the dust particles have uniform size, a uniform density within the dust cloud, and start with the same velocity a cross the magnetic field in the plasma's rest frame. The interaction is fou nd to be governed by a dimensionless parameter K which is a function of dus t cloud, and ambient plasma, parameters. For K much smaller than unity, the interaction goes on for typically 1/(2 piK) gyro times, with the particles in the dust cloud performing gyro motions with decreasing radius, For K cl ose to unity, the dust motion is stopped on the order of a dust particle gy ro time, For the case K much greater than 1, the plasma in the flux tube th rough the dust cloud is dragged across the magnetic field over a distance o f the order of Kr-d, where r(d) is the dust gyro radius, before the motion is stopped. Some expected effects for a more realistic dust cloud with density gradient s, and containing dust with a spread in size, are discussed. The results ha ve bearing on dusty plasma in space, e.g., models of the formation of spoke s in Saturn's ring system.