Nonlinear screening of dust grains and structurization of dusty plasma
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Y PLASMA
Nonlinear Screening of Dust Grains and Structurization of Dusty Plasma V. N. Tsytovich and N. G. Guseinzade Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 117991 Russia email: [email protected] Received April 24, 2012; in final form, October 17, 2012
Abstract—A review of theoretical ideas on the physics of structurization instability of a homogeneous dusty plasma, i.e., the formation of zones with elevated and depressed density of dust grains and their arrangement into different structures observed in laboratory plasma under microgravity conditions, is presented. Theoret ical models of compact dust structures that can form in the nonlinear stage of structurization instability, as well as models of a system of voids (both surrounding a compact structure and formed in the center of the structure), are discussed. Two types of structures with very different dimensions are possible, namely, those smaller or larger than the characteristic mean free path of ions in the plasma flow. Both of them are charac terized by relatively regular distributions of dust grains; however, the first ones usually require external con finement, while the structures of the second type can be selfsustained (which is of particular interest). In this review, they are called dust clusters and selforganized dust structures, respectively. Both types of the struc tures are characterized by new physical processes that take place only in the presence of the dust component. The role of nonlinearities in the screening of highly charged dust grains that are often observed in modern lab oratory experiments turns out to be great, but these nonlinearities have not received adequate study as of yet. Although structurization takes place upon both linear and nonlinear screening, it can be substantially differ ent under laboratory and astrophysical conditions. Studies on the nonlinear screening of large charges in plasma began several decades ago; however, up to now, this effect was usually disregarded when interpreting the processes occurring in laboratory dusty plasma. One of the aims of the present review was to demonstrate the possibility of describing the nonlinear screening of individual grains and take it into account with the help of the basic equations for the equilibrium between plasma components when analyzing equilibrium struc tures. The effect of plasma screening nonlinearity on both the diffusion processes and the forces of dust drag by plasma fluxes is analyzed. It is shown how selforganized dust structures form in these processes. In the limit of very small dust grain charges, the forces acting on the dusty plasma components and the set of basic equations for stationary dust structures (with allowance for nonlinear screening) take a standard form. New qualitative effects, such as the suppression of diffusion due to ion scattering from dust grains and the forma tion of structures of different configurations, are described. A detailed comparison with previous results is performed. It i
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