Resonant excitation of strong plasma wakefields by relativistic electron microbunches

We propose a self-consistent two-stage scheme for exciting ultra-high-gradient plasma wakefields via resonant interaction between a relativistic electron beam and plasmas. In the first stage, a low-density relativistic electron beam undergoes self-focusing and energy-chirp-induced betatron oscillations in an underdense plasma, spontaneously and self-consistently evolving into a train of periodic and dense microbunches. These in-situ formed microbunches are then injected into a denser plasma, where the microbunch period precisely matches the plasma wavelength, leading to resonant excitation of wakefields with peak amplitudes approaching 1 TV/m. Three-dimensional particle-in-cell (PIC) simulations confirm that microbunching periodicity matching the plasma wavelength is essential for maximizing the wakefield strength. By `self-shaping' the driver beam, our scheme significantly relaxes initial beam requirements, enhancing its robustness and feasibility for next-generation plasma accelerators.