Spectral properties of an N-pole helical structure consisting of like-charged equal-size dust grains

The oscillations and stability of an N-pole helical structure that consists of like-charged equal-size dust grains and is confined in a plasma in an axisymmetric potential well are studied theoretically. Self-confining structures, as well as their linear collective modes corresponding to three coupled types of grain displacements (change in the radius of the structure, change in the distance between neighboring lattice planes of the structure, and angular displacements in the lattice planes), are found. On the whole, the coupled oscillations have the form of wormlike perturbations. Dispersion relations for the oscillation modes of helical structures composed of N interwoven helices are derived and solved numerically