New results on the ion drag force in complex plasmas

Summary form only given. Ion drag force is known to be one of the most important forces acting on charged grains in complex plasmas, especially when the gravity is absent. Ion drag force and its competition with the electric force often determines the grain location in the discharge chamber, causes void formation in the experiments under microgravity conditions, affects the properties of low-frequency waves and the interaction between grains etc. Not surprisingly, considerable attention has been recently paid to the problem of accurate calculation of the ion drag in complex plasmas. In these papers the ion drag force was derived by calculating trajectories of ions scattered by the dust grain (assuming an isotropic screened Coulomb potential of interaction). This approach works well for collisionless ions and weakly anisotropic plasma (sub-thermal ion drifts). Here we report on the new calculations of the ion drag force using the linear dielectric response formalism. This approach allowed us to take into account ion-neutral collisions and anisotropies in ion-grain interaction potential caused by the ion flow (of arbitrary velocity) self-consistently. The role of these effects on the ion drag force is analyzed. Examples of ion drag calculations for typical complex plasma parameters are presented and the results are compared with experimental observations.