Phase Structural Transitions for Large 2D Dust Clusters in Complex Plasmas

Summary form only given. The field of complex plasmas has witnessed almost exponential growth since the discovery in 1994 of the self-assembly of ordered structures (Coulomb crystals) within a controlled lab environment. Recently there has been enormous interest in the static and dynamic behavior of 2- and 3D dust clusters consisting of a finite number of charged, ordered dust grains within a horizontal confinement. Both the resulting structures and the dynamic behavior of such small dust clusters (N<100) is now under intense investigation. It has recently been shown employing a numerical simulation that under certain conditions a structural phase transition can occur, reordering a 2D dust crystal from one exhibiting hexagonal lattice structure to that showing a spherical structure consisting of concentric rings. Such phase transitions appear to occur preferentially within the outer layers of larger dust clusters, where the Debye length and the confining potential both vary in a manner which is not yet completely understood. This paper examines such structural phase transitions, analyzing them quantitatively. Experimental data are also compared to simulation results.