External electron injection setup for the advanced wakefield experiment (AWAKE) run 2b

Abstract AWAKE is a plasma wakefield acceleration R&D experiment at CERN, where wakefields are driven by relativistic and self-modulated proton bunches. The goal of AWAKE Run 2b is to demonstrate that a correctly placed plasma density step stabilises the wakefield amplitude (after saturation of self-modulation) at a higher value than without the step. This can be demonstrated by accelerating witness particles. It is therefore planned to externally side-inject 19MeV test electrons into the wakefields. In this manuscript, the injection setup for the AWAKE Run 2b experiments is summarised. Challenges on beam transport due to the Earth’s magnetic field upstream of the vapour source entrance are highlighted and uncertainties on the injection location are estimated. Additionally, a new plasma-light-based diagnostic to verify that electrons cross the plasma column is introduced.