Ultrashort beam generation using Beam-Induced Ionization Injection in PWFAs*

Plasma wakefield accelerators (PWFA) have demonstrated acceleration gradients reaching tens of GeV per meter, showcasing their exceptional capabilities. Cutting-edge developments focus on producing high-quality beams via self-injection schemes and creating attosecond electron beams. This work presents a novel technique for injecting high-quality electron beams through beam-induced ionization injection (B-III) using a driver-injector beam configuration. In the B-III scheme, the drive beam's field intensifies as its slice envelope approaches its minimum due to betatron oscillations, releasing impurity plasma electrons for injection. We detail the analytical analysis of the injected beam's properties, including attosecond duration, hundreds of nanometers emittance, and less than 1% energy spread, supported by Particle-In-Cell (PIC) simulation results with FACET-II beam parameters. We also compare these results with those obtained from Lucretia, a physics toolbox that simulates electron beams through the FACET-II transportation line, to verify experimental feasibility. Lastly, we discuss the potential use of the injected beam in generating attosecond Free Electron Lasers (FEL).