Trapping and acceleration of relativistic electrons by uniform radially polarized Bessel-Gauss beams

This paper presents an efficient method for trapping and accelerating a 50 MeV relativistic electron beam in vacuum using radially polarized cylindrical vector Bessel-Gauss (BG) beams. Unlike conventional Laguerre-Gaussian (LG) beams, the non-diffracting property of BG beams extends the laser-electron interaction length, while their uniform field distribution enhances beam quality. The unique electric field structure of radially polarized light, featuring a strong longitudinal component, provides superior transverse confinement compared to circularly polarized beams, significantly reducing electron beam divergence. Three-dimensional particle-in-cell (PIC) simulations performed with the code EPOCH demonstrate that the electron energy increases from 50 MeV to 800 MeV, exhibiting less than 10.2% energy spread and a divergence angle below 1.5°. Further investigations reveal that higher laser intensity boosts electron energy without compromising beam collimation, while injection duration critically influences microbunch formation and maximum momentum. This approach offers a promising solution for compact high-energy electron accelerators, with potential applications in free-electron lasers and medical radiotherapy.