The Two-Screen Measurement Setup to Indirectly Measure Proton Beam Self-Modulation in AWAKE

摘要

The goal of the first phase of the AWAKE \cite{AWAKE1,AWAKE2} experiment atCERN is to measure the self-modulation \cite{SMI} of the $\sigma_z =12\,\rm{cm}$ long SPS proton bunch into microbunches after traversing$10\,\rm{m}$ of plasma with a plasma density of$n_{pe}=7\times10^{14}\,\rm{electrons/cm}^3$. The two screen measurement setup\cite{Turner2016} is a proton beam diagnostic that can indirectly prove thesuccessful development of the self-modulation of the proton beam by imagingprotons that got defocused by the transverse plasma wakefields after passingthrough the plasma, at two locations downstream the end of the plasma. Thisarticle describes the design and realization of the two screen measurementsetup integrated in the AWAKE experiment. We discuss the performance andbackground response of the system based on measurements performed with anunmodulated Gaussian SPS proton bunch during the AWAKE beam commissioning inSeptember and October 2016. We show that the system is fully commissioned andadapted to eventually image the full profile of a self-modulated SPS protonbunch in a single shot measurement during the first phase of the AWAKEexperiment.