Complex charge distributions of dielectric dust grains due to plasma flow

We examine the charging of dielectric dust grains embedded in a plasma. Our work is a continuation and refinement of our previous research into grain charging problems. In 1993, we discussed preliminary simulation results reg arding the charging and intergrain forces between two dielectric dust parti cles [J. W. Manweiler et al., Adv. Space Res. 13, 10175 (1993)]. then, in 1 996, we discussed preliminary results with respect to dust grain charging w ithin asymmetric plasma conditions and how these affect grain-grain collisi onal cross-sections [J. W. Manweiler et al., In: The physics of Dusty Plasm as (ed. P. K. Shukla et al.), p. 22. World Scientific, Singapore (1996)]. T his work was extended to evaluate how asymmetric charging affects coagulati on rates for dielectric dust grains [J. W. Manweiler et al., In: Physics of Dusty Plasmas, 7th Workshop (ed. M. Horanyi et al.), p. 12. AIP conf. Proc . 446 (1998)]. Here we report on the results of a significant refinement to our work to study the behaviour of a dielectric dust grain in a plasma wit h a bulk flow. Since charge transport is inhibited on our dielectric grains , we can examine how asymmetric plasma distributions affect the symmetry of the charge distributions that develop on the surfaces of the grains. A die lectric dust grain in a flowing plasma develops a negative total charge and a dipole moment in its charge distribution that points upstream. We also u se this model to study how the presence of a nearby dust grain affects the development of a grain's charge distribution. We demonstrate that a smaller grain-grain separation results in a reduced net charge on each grain. For grains in a flowing plasma, dipole moments are unaffected by close approach except when one grain is directly in the 'wake' of the other grain. The st udies here show that monopole and dipole electrostatic forces are present w hen dust is bathed in flowing plasma. Recent infrared studies suggest that a large fraction of young stars have dusty envelopes [G. Schilling, Science 286, 66 (1999)]. In the formation of accretion discs around young stars, d ust-plasma interactions are probably important. Full details on the calcula tions of the results discussed in this paper are summarized from a more com plete treatment of the subject by Manweiler [PhD Dissertation, University o f Kansas (1997)].