Narrow "Inception" Beams Generated in FACET Beam-Driven Wakefield Accelerator Setups

Although Plasma Wakefield Accelerators (PWFAs) can sustain accelerating gradients 100 times higher than conventional devices, the quality of the produced beams has been insufficient for future Free-Electron-Laser or Collider applications. To improve beam quality, through reducing energy spread, PWFAs typically operate in the beam-loaded nonlinear blowout regime. Here we show that in such regime, the accelerated beam can induce secondary ionization of plasma ions or neutral particles, and inject the released electrons into an additional low quality, high energy spread, beam called the "inception" beam. This work describes how the "inception" beam is formed in the PWFA that employs the Beam Induced Ionization Injection (BIII) technique. The supporting numerical study modeled the interaction of an electron beam with a hydrogen and helium gas, with the OSIRIS code, using the FACET beam parameters.