Fully self-consistent ion-drag force calculations for dust in   collisional plasmas with external electric field
  The ion-drag force on a spherical dust particle immersed in a flowing plasma with external electric field is self-consistently calculated using the Particle In Cell code SCEPTIC in the entire range of charge-exchange collisionality. Our results, not based on questionable approximations, extend prior analytic calculations valid only in a few limiting regimes. Particular attention is given to the force direction, shown never to be directed opposite to the flow except in the continuum limit, where other forces are of much stronger magnitude. 
Leonardo Patacchini and Ian H Hutchinson