Effect of trapped ions on shielding of a charged spherical object in a plasma

Collisions have traditionally been neglected in calculating the shielding a round a small spherical collector in a plasma, and the plasma flow to the c ollector. We show analytically that, in dusty plasmas under typical dischar ge conditions, ion charge-exchange collisions lead to the buildup of negati ve-energy trapped ions which dominate the shielding cloud in the nonlinear region near a dust grain and substantially increase the ion current to the grain, even when the mean-free path is much greater than the Debye length.