Density distribution in laser-cooled bunched beams

Knowledge of the density distribution of a bunched beam is important for controlling and damping instabilities which often depend on the distribution function (A.W. Chao, in Physics of Collective Beam Instabilities in High Energy Accelerators, Wiley, New York, 1993). In this paper, experimental studies of the longitudinal bunch shapes and temperatures of laser-cooled bunched beams are presented. These studies are combined with measurements of the transverse density distribution of the beam using a novel technique (Madsen et al., Proceedings of the Sixth European Particle Accelerator Conference, EPAC’98, Stockholm, IOP Publishing, Bristol 1998, p. 1046). The bunch shapes for various temperatures comply with a model where the transverse temperature is assumed to be high. However, in the longitudinally space-charge limited case, it is observed that the maximum attainable density is much lower than it would be in a completely space-charge limited beam. Furthermore, it is observed that this maximum density decreases with increasing current. These observations might be important for the beam quality obtainable with laser-cooling.