Description
Interest in the generation of electron-positron beams via electromagnetic showers has grown with the advent of multi-petawatt laser facilities (Apollon \cite{Apollon}, ELI Beamlines \cite{ELI}) and acceleration technologies. The near-term feasibility of such sources has motivated us to investigate the properties of pair jets generated through SFQED processes in the collision between ultra-relativistic electron beams ($1\leq \mathscr{E}_0\leq20$ GeV) and ultra-intense laser pulses ($100\leq a_0\leq500$). In this work, we characterize the density, dimensions, angular spread, and charge imbalance of the generated pairs as functions of both the initial electron bunch parameters and the laser pulse duration, field strength, beam waist, and polarization.
To account for realistic experimental conditions, the analysis of these produced pair observables is performed once the interaction between the laser pulse and the electron beam has ended. We identify the conditions for achieving maximum pair density in terms of the laser parameters. Our results, obtained with 3D Particle-In-Cell simulations in SMILEI \cite{smilei}, are supported by an analytical model based on the approach developed in \cite{ttys}. We show that comparing the short- and long-term evolution of the system with the time required for the initial electron bunch to radiate away all its energy enables the estimation of the number and spatial extent of the escaping pairs. This thereby provides a framework for optimizing density and establishing quantitative guidelines for future experiments.
\begin{thebibliography}{99}
\bibitem{Apollon} Papadopoulos \textit{et al.}, CLEO: Sci. Innov. \textbf{2019}, STu3E.4 (2019).
\bibitem{ELI} Weber \textit{et al.}, Matter Radiat. Extremes \textbf{2}, 149--176 (2017).
\bibitem{smilei} Derouillat \textit{et al.}, Comput. Phys. Commun. \textbf{222}, 351--373 (2018).
\bibitem{ttys} Pouyez \textit{et al.}, Phys. Rev. Lett. \textbf{134}, 135001 (2025).
\end{thebibliography}