Beam-Gas Interactions in the CERN Proton Synchrotron: Cross Section Measurements and Lifetime Modelling

Abstract

The acceleration of high-intensity lead (Pb) beams for injection into the Large Hadron Collider (LHC) is limited by significant losses in the preceding CERN ion injector chain. A potential but largely uncharted source of losses are charge-changing beam interactions such as electron loss or capture with residual gas molecules. These effects potentially impede future ion candidate species requested by the LHC and the CERN fixed-target experiments. To predict the cross sections of charge-changing processes and the corresponding ion beam lifetimes, we present a numerical implementation combining semi-empirical electron capture and loss formulae from previous studies. We verify this numerical model with an experimental PS benchmarking campaign, measuring various beam projectile lifetimes during interactions with two in-ring gas targets (argon, helium). The target pressure profiles are reconstructed in detail from gauge measurements and vacuum simulations. At higher injected gas pressures, where beam-gas interactions dominate, measured lifetime trends and derived cross sections converge with model predictions within reported semi-empirical uncertainties, validating the package for predicting impacts on current and future ion species.