Helical Electron Beam Micro‐Bunching by High‐Order Modes in a Micro‐Plasma Waveguide

). In particular, we demonstrate that when co-propagating with high-order waveguide modes, the electron can migrate transversely to keep up with accelerating brackets, leading to significant boost of the acceleration energy. This work paves the way towards the generation of high-charge, relativistic electron beams with controlled helicity, which holds great potential for advances in fundamental science and a variety of applications.