Coulomb balls : structure and confinement of spherical dust crystals in a plasma
In this thesis the fundamental properties of "Coulomb balls" are explored, a newly discovered form of spherical crystalline complex plasmas. Coulomb balls show an unusual type of structural order in complex plasmas, which is similar to laser-cooled ion clusters in Paul and Penning traps. A detailed analysis of the structural properties is presented. A comparison with molecular dynamics simulations revealed a significant influence of the plasma shielding on the structure. The confinement of Coulomb balls is based on the combination of two principles: First, dielectric walls, were used to shape the plasma profile and to generate a lateral confinement of the enclosed dust cloud. Second, a thermophoretic force is applied to compensate for gravity, which in combination with the plasma induced electric field force establishes a vertical confinement. The proposed functional principle of the trap used for confining Coulomb balls was quantitatively verified by means of measurements and simulations.