Energy-Spread Preservation and High Efficiency in a Plasma-Wakefield Accelerator

Energy-efficient plasma-wakefield acceleration of particle bunches with low energy spread is a promising path to realizing compact free-electron lasers and colliders. High efficiency can be achieved simultaneously by strong beam loading plasma wakefields when accelerating carefully tailored current profiles [M. Tzoufras et al., Phys. Rev. Lett. 101, 145002 (2008)]. We experimentally demonstrate such optimal in nonlinear electron-driven accelerator. Bunches an initial 1 GeV were accelerated 45 MeV energy-transfer $(42\ifmmode\pm\else\textpm\fi{}4)%$ at gradient $1.3\text{ }\text{ }\mathrm{GV}/\mathrm{m}$ while preserving per-mille spreads full charge coupling, demonstrating wakefield flattening the few-percent level.