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 $10^{11}$ and $3\times 10^{11}$ particles, various plasma density gradients ($-20\tilde{A}\cdot 20\%$) and two plasma densities ($2\times 10^{14}{\text{cm}}^{-3}$ and $7\times 10^{14}{\text{cm}}^{-3}$). The agreement is reached only in the case of a wide enough simulation box (at least five plasma wavelengths).

8 pages, 9 figures, 1 table