High quality electron bunch generation using a longitudinal density-tailored plasma-based accelerator

The feasibility of generating high quality electron bunches (high brightness, low energy spread and short duration) from a plasma-based accelerator that utilizes an appropriately tailored plasma density profile is demonstrated with three-dimensional particle-in-cell simulations. The underlying physical mechanism that leads to generation of high quality electrons is uncovered by tracking the particle trajectories of the electrons as they cross the sheath and are trapped by the wake. The intensity of the driver and the steepness of density profile select the electrons to be injected and determines the quality of the injected beam. In the given example, a peak brightness of $10^{19}$~A/m$^{2}$/rad$^{2}$ and a slice energy spread of $\sim 0.5~\mathrm{MeV}$ can be achieved by exciting a wake as the laser pulse traverses a plasma density downramp with a nominal density of $10^{19}$~cm$^{-3}$. Work supported by NSF and DOE.