On the possibility of measuring the forces of anisotropic interaction between macroparticles in a plasma with ion flow

Summary form only given. It is well known that a charged particle or macroobject, immersed in a flowing plasma, creates a perturbed region (a wake) behind itself. Wakefield potential is often invoked to explain a vertical alignment of dust particles levitating in the plasma sheath of capacitive radio-frequency (RF) discharge. In such a plasma ions have a directed velocity relative to stationary dust particles which in turn acquire a significant negative charge (103-104 elementary charges) due to the higher electron mobility. This can lead to focusing of ion fluxes behind particles and, as a consequence, to difference between the interaction of dust particles in the directions perpendicular to the ion flow and parallel to it. To date, the experimental determination of the pair interaction forces have been carried out between two horizontally aligned particles and between many particles of horizontal quasi-two-dimensional monolayer suspended in the sheath of capacitive RF discharge; as well as between heavy probe particle and dust cloud in the diffuse edge of inductive (electrodeless) RF discharge. In all the cases, the interparticle interaction can´t be described in the isotropic approximation. In this report we consider a possibility of experimental diagnostics of anisotropic interaction forces between dust particles in plasmas, arising due to effects of ion focusing. To recover anisotropic interparticle interaction forces we improved the method based on solving the inverse Langevin problem. We verified the method on the results of numerical simulation of chain structures of particles with quasidipole-dipole interaction, similar to the one occurring due to effects of ion focusing in gas discharges. It was shown that the proposed method can recover the spatial distribution of anisotropic interparticle interaction forces, and can be used for diagnostics of a laboratory dusty plasma with ion flow. An influence of charge spatial inhomogeneity and fluctuations on the r- sults of recovery is also discussed. For chain-like systems within which change in the charge of particles does not exceed 15%, the proposed method can be used without taking into account a spatial dependence of the particle charges. And fluctuations of the charges should not significantly affect on recovery of interparticle interaction forces at typical experimental conditions. The results also can be useful for other types of anisotropic interactions in dusty plasma systems, for example to study the properties of dust plasma with non-spherical dust particles.