New techniques for tailoring longitudinal density in a proton synchrotron", European Particle Accelerator Conf

The characteristics of the beam required for the Large Hadron Collider (LHC) impose stringent requirements on the CERN complex of injectors. A completely new scheme of operation, notably from the longitudinal standpoint, is foreseen for the Proton Synchrotron (PS) machine and its Booster (PSB) and has been tested in December 1993. It includes the original processes of “bunch flattening ” and “bunch splitting”. The first of these is applied in the PSB to reduce the space-charge induced transverse tune shift at injection in the PS. The second is employed in the PS to facilitate acceleration and debunching at high energy. Both techniques are described and the results achieved in December are presented and discussed. 1. NI-R~IXJ~TI~N The PS Complex, as part of the LHC injector chain, must provide a beam whose transverse particle density exceeds, by a factor of three, the highest currently attained yet must not be diluted by more than 20 % during its passage through the PS. The LHC scheme envisaged involves an upgrade of the PSB from 1 to 1.4 GeV, double-batch filling of the PS and new RF harmonics (h=l in the PSB, h=8 in the PS) [l, 21. The PSB routinely employs a second harmonic system to combat the space-charge induced (Laslett) tune shift from capture throughout the cycle and such a system (h=2) is foreseen in the LHC era. In addition, since beam will circulate in the PS for 1.2 s at the injection energy whilst awaiting a second batch from the PSB, an alternative technique for bunch flattening is under investigation. Bunch splitting (from h=8 to h=16) is required at the end of the PS injection plateau to reduce the peak beam current during acceleration and to improve the adiabaticity of debunching since, in the full LHC scheme, the beam must be rebunched on h=84 before extmction to the SPS