Structure and vertical modes in finite 2D plasma crystals

The formation of finite 2D plasma crystals was numerically simulated to allow the investigation of structural symmetries for systems with various Debye lengths. For the case of increasing Debye length, a transition was discovered between a fully hexagonal structure and a structure having concentric rings along the outer edge and a hexagonal lattice in the interior. Additionally, the vertical as well as horizontal oscillation modes in a thermally excited two-dimensional (2D) dust coulomb cluster were investigated. The horizontal mode spectra is shown to agree with published results while the vertical mode spectra obtained from numerical simulation is shown to agree with current data from analytical methods. The vertical mode frequencies are shown to have a maximum corresponding to when the system acts as a solid plane. For low frequency modes, the largest amplitude particle motion is concentrated within a few inner rings with the outer rings remaining almost motionless. This provides an interesting contrast to the horizontal mode frequencies for which the strongest motion of the particles is concentrated within the inner rings at high frequencies.