Unveiling the beam-wake interactions in plasma wakefield acceleration

Plasma wakefield accelerators, powered by high-current particle beams, promise compact and cost-effective sources of energetic leptons for future light sources and particle colliders. The interplay between the driving particle bunch and the plasma wakefields fundamentally determines accelerator performance. Gaining direct insight into these interactions is therefore key to realizing high-efficiency, high-quality particle acceleration. Using femtosecond ultrarelativistic electron microscopy, we characterize in situ both the wakefield and the driving bunch from a single-shot image with unprecedented detail. By systematically varying the driver charge, we capture the transitions from linear to nonlinear wakefield regimes. We also observe beam-wake coupling manifested through wakefield flattening and transverse dynamics of the driving bunch. These observations provide crucial real-time insights into the highly transient and complex dynamics of beam-plasma interactions, paving the way for precise control of the acceleration process.