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
regarding the charging and intergrain forces between two dielectric dust
particles [J. W. Manweiler et al., Adv. Space Res. 13,
10175 (1993)]. Then, in
1996, we discussed preliminary results with respect to dust grain charging
within asymmetric plasma conditions and how these affect grain–grain
collisional cross-sections [J. W. Manweiler et al., In: The Physics of Dusty
Plasmas (ed. P. K. Shukla et al.), p. 22. World Scientific, Singapore (1996)].
This work was extended to evaluate how asymmetric charging affects
coagulation 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 with 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 dielectric dust grain in
a flowing plasma develops a negative total charge and a dipole moment in its
charge distribution that points upstream. We also use 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 studies here show that monopole and dipole
electrostatic forces are present when dust is bathed in flowing plasma. Recent
infrared studies suggest that a large fraction of young stars have dusty
envelopes [G. Schilling, Science286, 66 (1999)].
In the formation of accretion
discs around young stars, dust–plasma interactions are probably important.
Full details on the calculations of the results discussed in this paper are
summarized from a more complete treatment of the subject by Manweiler [PhD
Dissertation, University of Kansas (1997)].
Modelling an isolated dust grain in a plasma using matched asymptotic expansions