Systematic optics studies for the commissioning of the AWAKE electron beamline

The commissioning of the AWAKE electron beam line was successfully completed in 2018. Despite a modest length of about 15 m, this low-energy line is quite complex and several iterations were needed before finding satisfactory agreement between the model and the measurements. The work allowed to precisely predict the size and positioning of the electron beam at the merging point with the protons inside the plasma cell, where no direct measurement is possible. All the key aspects and corrections which had to be included in the model, precautions and systematic checks to apply for the correct setup of the line are presented. The sensitivity of the ∼18 MeV electron beam to various perturbations, like different initial optics parameters and beam conditions, energy jitters and drifts, earth’s magnetic field etc., is described.