Experiments with low intensity beams of electron-cooled highly charged ions in the storage ring ESR have been performed. The momentum spread which was analyzed by Schottky noise detection shows a considerable reduction when the number of stored ions is reduced below several thousands. This indicates that intrabeam scattering which determines the momentum spread for higher beam intensities is strongly suppressed. Estimates of the plasma parameter $\gamma$ support the idea of a phase transition from a gaseous phase to a liquidlike phase.

• Received 28 June 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.3803