Eight charged particles in the Ring Trap.  The outer ring is about 20 mm in diameter, and the scene is illuminated with green laser light.  Trapped particles oscillate at 60 Hz, and this long-exposure photograph shows tracks that delineate the path of each particle.  The particles all have like charges, so their mutual repulsion keeps them apart, while at the same time trapping forces push the particles toward the trap center.  The resulting lattice-like structure is called a Coulomb crystal.

Electrodynamic Ion Traps