Transition of Small Debye Clusters from Two Dimensions to One Dimension
A Debye cluster is a group of n dust particles in a plasma interacting through a shielded Coulomb (i.e., a Debye) potential. Clusters form a two-dimensional ellipse when they are confined by the anisotropic potential well introduced by a rectangular trap. It is expected that as the well anisotropy increases, the elliptical cluster will become elongated and at some point all the particles will lie in a straight line so that the cluster is fully one dimensional. Experiments performed in the DONUT experiment (Dusty Ohio Northern University experimenT) for two confinement geometries and for n = 2 to 24 particles have shown the stages of the two-to-one dimensional transition. We find that as the number of particles decreases, the two-dimensional ellipse shrinks and then grows two linear tails forming a “barred elliptical” cluster. For n = 6 clusters are fully one dimensional.