New evidence for one-dimensional ordering in fast heavy ion beams

Abstract

Experiments at the experimental storage ring with electron-cooled heavy ionbeams have shown that at low beam intensity the beam enters a newregime. A transition to a state different from the normal gaseous state ofthe beam, which is determined by an equilibrium between intrabeamscattering and electron cooling, was made apparent by a sudden reductionof the momentum spread by up to one order of magnitude. Recently adestructive method to measure the horizontal beam size by beam scrapinghas been developed to a resolution of micrometres. Application of thismethod to the low intensity beam below the transition point has indicated asimultaneous reduction of the beam size by even more than an order ofmagnitude. A likely explanation is the formation of a one-dimensionalordered structure at low intensity. The stability of this ordered state againstintrabeam scattering or other heating sources has been confirmed by directobservation of the beam in the low intensity regime after an intentionaldeactivation of cooling. The uncooled low intensity beam remains for millions ofrevolutions in the storage ring in the cold state, in contrast to beam intensitiesabove the transition point for which an immediate heating is observed.