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Abstract

Intense high-energy particle beams are used in fundamental sciences, material sciences,
relativistic laboratory astrophysics, and in the industry. Traditionally, dense collimated
multi-GeV photon and electron-positron beams are generated via bremsstrahlung and
Bethe-Heitler (BH) electron-positron pair creation, respectively. Recent research has
focused on strong-field QED processes for greatly enhancing the flux and intensity of
the generated beams. To determine the relative role of collisional and strong-field
QED processes, we implemented bremsstrahlung and BH pair production processes in
the particle-in-cell code Smilei. Using simulations, we show that a high-current ultrarelativistic
electron beam interacting with a submicrometer-thick conducting foils can
undergo strong self-focusing accompanied by efficient emission of gamma-ray photons.
We study the effect of varying electron beam shape, radius and length on the final radiated
energy. We show that the self-generated fields can be strong enough that emission
occurs in the strong-field QED regime, where a single emitted photon can carry away
a significant fraction of the emitting electron energy. We demonstrate that, after beam
collision with multiple foils, femtosecond collimated electron and photon beams with
particle number density exceeding that of a solid are obtained. This study is timely as
it enables laserless strong-field QED investigations with a single high-current electron
beam, particularly relevant for the upcoming FACET II facility.