Self-consistent calculations of the electric charge, ion drag force, and the drift velocity of spherical dust grains immersed in collisional ion flows using Langevin Dynamics and comparisons against canonical experimental data*

We present a trajectory simulation-based modeling approach to capture the interactions between ions and charged grains in dusty or complex plasmas (gas discharges containing dust grains). Our study is motivated by the need for a self-consistent and experimentally validated modelling approach for accurately calculating the ion drag force and grain charge that are important in the grain collective behavior in plasmas. We implement Langevin Dynamics in a computationally efficient predictor-corrector approach to capture multiscale ion and grain dynamics. Predictions of grain velocity, grain charge, and ion drag force are compared with prior measurements to assess our approach. The comparisons reveal excellent agreement within <!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>±20%  between predicted and measured grain velocities (Phys. Plasmas 12(9): 093503) for <!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>0.64, 1.25 μm  grains at <!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>~20-120 Pa . Comparisons with the measured grain charge (Phys. Rev. E 72(1): 016406) under similar conditions reveal agreement to within <!--[if gte msEquation 12]>~20%  as well. Measurements of the ion drag force (Phys. Plasmas 11(12): 5690 and IEEE Trans. Plasma Sci. 32(2): 582) are used to assess the viability of the presented approach to calculate the ion drag force experienced by grains exposed to ion beams of well-defined energy. Excellent agreement between calculations and measurements is obtained for beam energies >10 eV and the overprediction below 10 eV is attributed to the neglect of charge exchange collisions in our modeling. Along with critical assessments of our approach, suggestions for future experimental design to probe charging of and momentum transfer onto grains that capture the effect of ion and grain number concentration are outlined.