Study of Transverse and Longitudinal Wakefields Driven by a Long Proton Bunch

Self-modulation of a long, relativistic, charged particle bunch in a dense plasma is an interesting beam/plasma interaction mode and a means to drive large amplitude wakefields ($>$1\,GV/m) for particle acceleration.\footnote{ N. Kumar et al., Phys. Rev. Lett. 104, 255003 (2010)} % By measuring the effect of transverse wakefields on the drive proton bunch, we learn about the development of transverse wakefields over the first 4\,m of plasma. % By measuring energy gain by externally injected electrons, we learn about longitudinal wakefields over the last 5\,m of plasma. % Combining these results for various experimental parameters, we conclude that experimental results are consistent with simulation ones that show the SM process saturates before the end of the 10\,m plasma.\footnote{M. Turner, P. Muggli et al., (AWAKE Collaboration) submitted to PR-AB (2020)} % This is a key piece of information for future AWAKE experiments\footnote{P. Muggli et al., (AWAKE Collaboration) Plasma Phys. and Contr. Fus., 60(1) 014046 (2017)} that will use a first, 10\,m-long plasma as self-modulator. % Acceleration will occur in a second plasma. % We present detailed experimental and simulation results. %