Near-GeV Electron Beams at a Few Per-Mille Level from a Laser Wakefield Accelerator via Density-Tailored Plasma

A simple, efficient scheme was developed to obtain near-gigaelectronvolt electron beams with energy spreads of few per-mille level in a single-stage laser wakefield accelerator. Longitudinal plasma density was tailored to control relativistic laser-beam evolution, resulting in injection, dechirping, and a quasi-phase-stable acceleration. With this scheme, electron beams with peak energies of 780--840 MeV, rms energy spreads of 2.4\mbox{\textperthousand}--4.1\mbox{\textperthousand}, charges of 8.5--23.6 pC, and rms divergences of 0.1--0.4 mrad were experimentally obtained. Quasi-three-dimensional particle-in-cell simulations agreed well with the experimental results. The dechirping strength was estimated to reach up to $11\text{ }\text{ }\mathrm{TeV}/\mathrm{mm}\mathrm{/m}$, which is higher than previously obtained results. Such high-quality electron beams will boost the development of compact intense coherent radiation sources and x-ray free-electron lasers.