Simulations of X-ray free-electron-lasers driven by plasma-based acceleration*

Plasma-based acceleration can provide high-energy electrons in a very short distance, which can much shrink the size and reduce the cost of the transformative modern machine – X-ray free-electron-lasers. However there are many challenges needed to be overcome before plasma wakefields can generate electrons with the required beam quality (brightnesses and low energy spreads) inside the wake and before these beams can be transported from the plasma to the undulator without beam quality degradation. We will present our recent progress from particle-in-cell simulations and theory on this topic, including concepts for producing high energy beams with unprecedented normalized brightnesses using density down ramp injection in the three-dimensional nonlinear blowout regime, matching the beam out of the plasma using longitudinally tailored plasma profiles, and start-to-end simulations of such plasma wakefied accelerators driven X-ray free-electron-lasers.