Characterisation of transverse proton beam losses at the CERN Super Proton Synchrotron

The High-Luminosity LHC (HL-LHC) project foresees nearly doubling the design beam intensity of CERN's Large Hadron Collider (LHC). A particularly pressing issue is the observation of significant beam losses at the flat bottom in the Super Proton Synchrotron (SPS) that delivers these beams to the LHC. These losses arise from multiple factors: uncaptured beam losses that are generated during the bunch rotation in the Proton Synchrotron (PS) before the transfer to the SPS; large transient beam loading effects in the RF system during multi-turn SPS injections; and the diffusion of over-populated transverse tails, which reach aperture limitations. Dedicated beam measurements were carried out in the SPS as a first step towards untangling these losses. These studies aimed to disentangle the various loss mechanisms, with a focus on the halo population and potential correlations between transverse and off-momentum tails.