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

TL;DR

This paper presents a numerical model for predicting charge-changing cross sections and beam lifetimes in the CERN Proton Synchrotron, validated through experimental measurements with gas targets, aiding future ion beam optimization.

Contribution

It introduces a validated numerical implementation combining semi-empirical formulas to predict beam-gas interaction effects on ion beam lifetimes at CERN.

Findings

Model predictions agree with experimental data within uncertainties.

Validated the model using measurements with argon and helium gas targets.

Demonstrated the model's usefulness for future ion species and accelerator planning.

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.