• H. Damerau, S. Hancock, M. Schokker
  CERN, Geneva

As one of the pre-injectors for the Large Hadron Collider, the CERN Proton Synchrotron must reliably deliver a wide range of beam parameters. The large variety of bunch spacings from 25 to 150 ns at extraction requires the acceleration of small, high-density bunches as well as highly intense ones. Above a threshold bunch density, longitudinal coupled-bunch instabilities are observed after transition crossing and the main accelerating cavities have been identified as part of the impedance driving them. Transient beam loading causes asymmetries of the various bunch splittings used to establish the required bunch spacing, compromising beam quality at the head of the bunch train delivered. Recent measurements and longitudinal limitations of beams for the LHC are presented, together with possible cures and options for future hardware improvements.