Energy-spread preservation and high efficiency in a plasma-wakefield accelerator

Lindstrøm, C. A. and Garland, J. M. and Schröder, S. and Boulton, L. and Boyle, G. and Chappell, J. and D'Arcy, R. and Gonzalez, P. and Knetsch, A. and Libov, V. and Loisch, G. and Martinez De La Ossa, A. and Niknejadi, P. and Põder, K. and Schaper, L. and Schmidt, B. and Sheeran, B. and Wesch, S. and Wood, J. and Osterhoff, J. (2021) Energy-spread preservation and high efficiency in a plasma-wakefield accelerator. Physical Review Letters, 126 (1). 014801. ISSN 0031-9007

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    Energy-efficient plasma-wakefield acceleration of particle bunches with low energy spread is a promising path to realizing compact free-electron lasers and particle colliders. High efficiency and low energy spread can be achieved simultaneously by strong beam loading of plasma wakefields when accelerating bunches with carefully tailored current profiles [M. Tzoufras, Phys. Rev. Lett. 101, 145002 (2008)PRLTAO0031-900710.1103/PhysRevLett.101.145002]. We experimentally demonstrate such optimal beam loading in a nonlinear electron-driven plasma accelerator. Bunches with an initial energy of 1 GeV were accelerated by 45 MeV with an energy-transfer efficiency of (42±4)% at a gradient of 1.3 GV/m while preserving per-mille energy spreads with full charge coupling, demonstrating wakefield flattening at the few-percent level.