Longitudinal phenomena in the CERN SPS

After almost one year of operation two kinds of problems dominate the longitudinal behaviour of the SPS beam. At high energy longitudinal coupled bunch instabilities occur. They are driven by the RF cavity impedance both on its fundamental and high-order passbands. Present cures include damping the high-order modes of the cavities, Landau damping techniques and feedback systems. At the injection energy a debunching-rebunching procedure is performed in order to change from the 9.5 MHz RF frequency of the injector to the 200 MHz of the SPS. Debunched beam instabilities driven by the cavity and vacuum chamber impedances (up to the GHz region) at present limit the RF capture efficiency. (13 refs).