Charge coupling in multi-stage laser wakefield acceleration

摘要： The multi-stage technique in the laser driven acceleration of electrons has become a critical part for full-optical jitter-free accelerators. Several independent laser drivers and shorter plasma targets allow the stable and reproducible acceleration of electron bunches (or beam) at the GeV energies with narrower energy spreads. Moreover, the charge coupling, necessary for ef?cient acceleration in the consecutive acceler-ation stages, depends collectively on the parameters of the injected electron beam, the booster stage, and the nonlinear transverse dynamics of the electron beam in the laser pulse wake. An unmatched electron beam injected in the booster stage and its nonlinear transverse evolution may result in perturbations and even a reduction of the ?eld strength in the acceleration phase of the wake?eld. Thus, the analysis and characterization of charge coupling in multi-stage laser wake?eld acceleration (LWFA) are important. Here, we investigate acceleration of an externally injected electron beam in the laser wake?eld, emulating two-stage LWFA, using fully relativistic multi-dimensional particle-in-cell simulations. We also study the underlying critical parameters that affect the ef?cient coupling and acceleration of the injected electron beam in the booster stage.