Dipole-dipole interactions between dust grains in plasmas

Complete screening of the negative dust grain charge by a cloud of trapped ions in plasmas is investigated. In the plasma electric field, the compound dust particle “dust grain + ion cloud” acquires a dipole moment due to displacement of the centers of positive and negative charges in the opposite directions within the compound particle. By analogy to the van der Waals attractive interaction potential, the dipole-dipole interactions of the compound dust particle can have an attractive behavior. It is shown that, for the electric field strengths typically observed in experiments, the dipole-dipole attractive force exceeds the shadowing force that is connected with the reciprocal interception of ions by the neighboring dust grains.