Large-bandwidth x-ray free-electron-laser (XFEL) facilities are desirable scientific tools in various fields, such as molecular structural dynamics and spectroscopy diagnosis. Various methods are proposed to broaden the FEL spectra. Here, a method is proposed to generate high-power XFEL radiation of tunable spectral bandwidth using plasma wakefield acceleration. An ultrabroad bandwidth is achieved by chirping the electron beam in a hollow-channel plasma without noticeable slice-beam-quality degradation. A dedicated beamline can match the beams with a large energy chirp in the undulators almost without beam loss. Numerical simulations demonstrate that a relative spectral bandwidth (full width) of up to 24% can be obtained with optimized beam and plasma parameters.

• Received 29 August 2022
• Revised 24 December 2022
• Accepted 11 April 2023

DOI:https://doi.org/10.1103/PhysRevApplied.19.054066