Proton beam defocusing in AWAKE: comparison of simulations and measurements

Abstract

In 2017, AWAKE demonstrated the seeded self-modulation (SSM) of a 400 GeV proton beam from the Super Proton Synchrotron (SPS) at CERN. The angular distribution of the protons deflected due to SSM is a quantitative measure of the process, which agrees with simulations by the two-dimensional (axisymmetric) particle-in-cell code LCODE. Agreement is achieved for beam populations between 1011 and 3×1011 particles, various plasma density gradients (−20 ÷ 20%) and two plasma densities (2 × 1014cm−3 and 7 × 1014cm−3 ). The agreement is reached only in the case of a wide enough simulation box (at least five plasma wavelengths).