Figure 1. Beamloading of the plasma wake in 1D nonlinear regime.

On-axis longitudinal electric field E_z (blue line) and electrostatic potential φ (dashed black line) in a plasma wave of density n₀=1.1 × 10¹⁷ cm⁻³, driven by a non-evolving electron beam (red curve), propagating to the right. Adding an electron escort beam (green curve) with charge density n_b can load the wake and flatten or reverse the electric longitudinal field locally: (a) unloaded case (n_b=0), where the position of the witness bunch n_w (purple curve) and its resulting energy chirp is indicated schematically, (b) n_b/n₀=0.5, (c) n_b/n₀=1.0 and (d) n_b/n₀=1.5. The results are obtained using the 1D nonlinear fluid model description. The electron witness bunch position and size (purple) is indicated, thus visualizing the electric accelerating field which would be sampled by the witness. The insets in (a,d) are the longitudinal phase spaces of the witness bunch, indicating the phase rotation for the (a) unloaded and (d) loaded cases.