Coulomb double helical structure.

Structures of Coulomb clusters formed by dust particles in a plasma are studied by numerical simulation. Our study reveals the presence of various types of self-organized structures of a cluster confined in a prolate spheroidal electrostatic potential. The stable configurations depend on a prolateness parameter for the confining potential as well as on the number of dust particles in a cluster. One-dimensional string, two-dimensional zigzag structure and three-dimensional double helical structure are found as a result of the transition controlled by the prolateness parameter. The formation of stable double helical structures resulted from the transition associated with the instability of angular perturbations on double strings. Analytical perturbation study supports the findings of numerical simulations.

Rotation of a two-dimensional Coulomb cluster in a magnetic field.

A coordinated study of a laboratory experiment, a computer simulation, and a theoretical analysis reveals a structure and its dynamic motion of a Coulomb cluster trapped in a plasma with a confining potential in the presence of gravitational and magnetic fields. Charged dust particulates are found to form a circle in a horizontal plane with a radius determined by a balance of a restoring force due to a confining potential and the screened Coulomb force between dust particulates. The dust particulates in a circle show angular rotation with the structure intact, while they oscillate radially around the equilibrium orbit. The analytical study reveals the oscillatory rotational nature of dust particulates as a result of coupling between the Lorentz force and the harmonic oscillation.