Beam Loss Reduction by Barrier Buckets in the CERN Accelerator Complex

For a future intensity increase of the fixed-target beam in the accelerator complex at CERN, new techniques to reduce beam loss are required. A major fraction of the losses during extraction of the coasting beam from the PS towards the SPS originate from poorly kicked particles during the Multi-Turn Extraction. A line density depletion, synchronised with the extraction kickers, decreases these losses significantly when successfully combined with the present extraction scheme involving the transverse splitting of the beam. The Finemet wide-band cavity recently installed in the PS as a longitudinal feedback kicker was used to generate a so-called barrier bucket, which is utilised to deplete the line density and reduce the losses. The drive to generate the barrier bucket waveform synchronously with the beam was developed and installed by the radiofrequency cavity as part of these studies. The effectiveness of the combination of the Multi-Turn Extraction and the barrier bucket was evaluated with beam. This manipulation was performed for the first time in a particle accelerator. The measured data with beam in the CERN PS shows a substantial, up to an order of magnitude beam loss reduction at extraction, even well beyond the standard operational beam intensity. This means that the combination of the Multi-Turn Extraction with the barrier buckets achieves a practically loss-less extraction for the fixed target beam from the PS. Based on the results of the measurements and simulations with beam, a concept for the synchronisation between the CERN PS and SPS accelerators is also presented to realise the beam loss reduction in future operation.