Fig. 1: Sketch of the experiment.
From: Recovery of hydrogen plasma at the sub-nanosecond timescale in a plasma-wakefield accelerator
The pump electron beam moves in the plasma undergoing deceleration. Depending on the plasma (np) and beam (nb) densities, the ions stay mostly unperturbed (a) or are pinched (b, generating larger np). This affects the probe beam (delayed by Δt with respect to the pump) whose deceleration is proportional to np. The two plasma-modulated longitudinal phase-spaces highlight the different signatures on the probe.
