X-ray Free-Electron Laser accelerator to study on Quantum Electro-Dynamics

X-ray free-electron lasers (XFELs) utilize high-density and high-energy electron bunches which are well-suited to produce Compton back-scattering radiation. Here we study study interaction of such electron bunches during head-on collision with retroreflected X-ray pulses, emitted by an XFEL. Such collisions allow one to conduct experiments on electron-positron pair production, both through trident and gamma-gamma colliding processes. We discuss cost-effective setups to study such processes, taking advantage of the existing conventional as well as proposed X-ray FEL infrastructure. We estimate parameters of the proposed experiments and compare them with other projects under construction.