String structures in driven 3D complex-plasma clusters

¹ Max Planck Institute for Extraterrestrial Physics - Giessenbachstraße, D-85748 Garching, Germany, EU
² Groupe de la Recherche sur l'Energie et les Materiaux Ionisées - F-84677 Orléans, Cedex 2, France, EU
³ Christian-Albrechts Universität zu Kiel - D-24118 Kiel, Germany, EU

Received: 14 September 2012
Accepted: 15 October 2012

Abstract

The structure of driven three-dimensional complex-plasma clusters was studied experimentally. The clusters consisted of around 60 glass microspheres that were suspended in a plasma of rf discharge in argon. The particles were confined in a glass box with conductive yet transparent coating on its four side walls. This allowed manipulating the particle cluster by biasing the confining walls in a certain sequence and direct imaging of the cluster. In this work, a rotating electric field was used to drive the clusters. Depending on the field frequency, the clusters rotated (10⁴–10⁷ times slower than the rotating field) or remained stationary. The cluster structure was neither that of nested spherical shells nor a simple chain structure. Strings of various lengths were found consisting of 2 to 5 particles, their spatial and temporal correlations were studied. The results are compared to recent simulations.