Transverse Instabilities of the LHC Proton Beam in the SPS

The availability from the injectors of the proton beam required for the LHC era has allowed studying its transverse behaviour in the SPS. Profile and beam oscillation measurements evidenced the existence of strong transverse instabilities developing along the batch and inducing an emittance blow-up of increasing importance from the head to the tail of the batch. An intensity threshold, comparable to that observed for the development of the beam induced electron cloud, has been found for the onset of the above phenomena. The results of the measurements and their possible interpretation are presented.