RESUMO
A technique has been developed to derive the dynamic properties of an ensemble of particles in dusty plasmas by using fluorescent tracer particles. The tracers form an integral part of the entire dust system. The dynamic properties of the dust system is reconstructed from the motion of the tracer. This technique allows long-duration experiments and is applied to a two-dimensional Coulomb cluster where the flow field, intershell rotation, and stagnation points of the flow have been identified.
RESUMO
The melting transition of finite three-dimensional dust clouds (Yukawa balls) from a solid-like to a liquid-like state is systematically studied with high spatial and temporal resolution of the individual grains by means of stereoscopy. Two different melting scenarios are reported: Melting is induced first by an increase of plasma power, and second by laser-induced heating. The experiments confirm that melting starts with a loss of orientational correlation, followed by a loss of the radial order upon further heating. While the plasma-power melting is driven via the ion wakefield, laser heating provides a more equilibrium scenario. The internal loss of correlations is well captured by the triple correlation function (TCF) which is insensitive to particle exchanges and the rotation of the cluster as a whole. The critical Coulomb coupling parameter for N=35 is determined as Γ(crit)≈570. The experimental findings are in good agreement with thermodynamic Monte Carlo simulations.