New Methods to Create Hollow Bunches

New methods to create hollow distributions in longitudinal phase space based on manipulations with a double harmonic RF system at high energy are presented with application to the PS Booster synchrotron (PSB). Whereas the first tenatative to create hollow bunches at the PSB aimed to improve the performance of the PSB itself, these new methods are expected to reduce the limitations due to direct space charge forces in the receiving PS (where no double harmonic RF system is available) after transfer. One method aims to introduce empty phase space in the centre of the phase space by recombination of the beam in one bucket with another empty bucket. The second method is based on redistribution of phase space surfaces during the transfer of the beam from one second harmonic sub-bucket to another. During that process, phase space surfaces are exchanged and low density from the periphery ends up in the centre, whereas the high density surfaces from the centre are transferred to the periphery. Both methods have been simulated by particle tracking. The second method has been applied in practice at the PSB. The set-up turned out to be simple and fast, and to yield hollow distributions with good reproducibility.