Electron beam scattering in Rubidium vapour at AWAKE

Abstract The Advanced Wakefield Experiment (AWAKE) at CERN uses bunches from the CERN SPS to develop proton-driven plasma wakefield acceleration. AWAKE Run 2c (starting in 2029) plans for external on-axis injection of a 150MeV electron witness bunch with the goal to demonstrate emittance control of multi-GeV accelerated electron beams. Prior to injection, the electron witness bunch may have to traverse rubidium vapour. Since the beam must have the correct beam size and emittance at injection, it is important to quantify the scattering effect. For this, first-principle estimates and G eant 4 simulations are compared with measurements of a ∼20MeV electron beam scattering in 5.5m of rubidium vapour, showing good agreement. Building on this agreement, G eant 4 simulations using the estimated AWAKE Run 2c parameters are performed. These predict that scattering will not increase the electron beam size or emittance.