Stability and dynamics of ion rings in linear multipole traps

Trapped singly-charged ions can crystallize as a result of laser cooling. The emerging structure depends on the number of particles and on the geometry of the trapping potential. In linear multipole radiofrequency traps, the geometry of the radial potential can lead to the formation of single-ring structures. We analyse the conditions and stability of single rings as a function of the number of poles. For larger numbers of ions the rings form tubes in which the arrangement of the ions corresponds to a triangular lattice folded onto a cylinder. The stability of these tubular structures is numerically studied for different lattice constants and their normal mode spectrum is determined.