To advance the development of a stable laser wakefield accelerator (LWFA) for free-electron laser (FEL) applications, we established a novel LWFA platform at the RIKEN SPring-8 Center. By combining precise injection control, laser wavefront stabilization, and optimized gas-jet performance, together with careful tuning of phase rotation and beam loading, we generated quasi-monoenergetic electron beams with an energy spread below 1%, pointing stability better than 0.5 mrad, energy stability better than 6%, and a central energy of 400 MeV. Injection of these beams into a mini-undulator successfully demonstrated FEL amplification in the XUV range, achieving a gain factor of 20. More recently, further refinements of the experimental environment have resulted in improved electron-beam stability, further strengthening the potential of this platform for reliable FEL operation.

wakefield acceleration, shock injection, FEL