Bunch shaping in electron linear accelerators

Electron beams from modern high performance accelerators power intense light sources such as free electron lasers and synchrotron light sources, as well as wakefield-based accelerating modules relying on plasmas or dielectric structures. The way the electron bunches are shaped in space and time controls the efficacy of how the electron beam radiates or interacts with structures. In this review the physics behind methods for controlling the mesoscopic electron-bunch properties, i.e., phase-space distributions, from an electron accelerator are discussed, from both a theoretical and an experimental perspective. The focus is on phase-space shaping methods relying on bounded external electromagnetic fields or self-generated velocity and radiation fields, and how they are implemented.