Observation of transverse space charge effects in a mutli-beamlet electron bunch produced in a photo-emission electron source

A "multiple beamlet" experiment aimed at investigating the transverse space charge effect was recently conducted at the Argonne Wakefield Accelerator. The experiment generated a symmetric pattern of 5 beamlets on the photocathode of the RF gun with the drive laser. We explored the evolution of the thereby produced 5 MeV, space-charge dominated electron beamlets in the 2m drift following the RF photocathode gun for various external focusing. Two important effects were observed and benchmarked using the particle-in-cell beam dynamics code Impact-T. In this paper, we present our experimental observation and their benchmarking with Impact-T.