Evolution of voids in dusty plasmas

Abstract

It is shown that formation of dust voids is a general phenomenon in dusty plasmas. Homogeneous dusty plasmas are universally unstable for formation of dust voids and dust structures. Both collision-dominated and collision-less voids can be formed. They are distinguished by the ratio of the void size to the ion-neutral collision mean free path being either large or small, while the mean free path for dust-ion collisions in both cases is small or comparable with the void size. The boundary which separates the dust region from the dust-free region is always sharp as compared to the void size for low ratio of dust temperature Td to ZdTe (Te is the electron temperature and Zd is the dust charge in units of electron charge). It is shown that stationary voids are stable for large deviations from equilibrium size. A review is given on theoretical and numerical investigations of both collision-dominated and collision-less voids together with a comparison with experimental results and observations in space. Investigation is performed of voids in presence of floating potential boundaries. Both flat and spherical voids are considered. Dusty plasma experiments in micro-gravity are computer modeled and necessary conditions for the dusty plasma structure formation are found. A condition is that the structure should be separated from the floating potential wall by a void. Presence of a void region between the dust structure and the wall is shown to be necessary for structures to be formed. These voids are different both from the voids in absence of boundaries and from collisional sheaths in absence of dust. Properties of these voids are investigated. Computer experiments for micro-gravity dusty plasmas shows the possibility of creation of almost homogeneous self-confined dust structures surrounded by voids with properties determined by the dust structure.