Charge coupling in multi-stage laser wakefield acceleration

Abstract

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 efficient acceleration in the consecutive acceleration 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 field strength in the acceleration phase of the wakefield. Thus, the analysis and characterization of charge coupling in multi-stage laser wakefield acceleration (LWFA) are important. Here, we investigate acceleration of an externally injected electron beam in the laser wakefield, emulating two-stage LWFA, using fully relativistic multi-dimensional particle-in-cell simulations. We also study the underlying critical parameters that affect the efficient coupling and acceleration of the injected electron beam in the booster stage.