Onset of electron-seeded cascades in generic electromagnetic fields

TL;DR

This paper develops a generalized theory for the onset of QED cascades in arbitrary electromagnetic fields, enabling predictions of cascade initiation and potential applications in generating high-energy photon beams.

Contribution

It introduces a general expression for the short-time behavior of electron quantum parameters, extending the threshold condition for QED cascade onset in various field configurations.

Findings

A new criterion for cascade initiation in arbitrary fields.

Simulation results show seed electron bunches can trigger self-sustained cascades.

Potential to produce high-energy collimated photon beams.

Abstract

QED cascades in a strong electromagnetic field of optical range and arbitrary configuration are considered. A general expression for short-time dependence of the key electron quantum dynamical parameter is derived, allowing to generalize the effective threshold condition of QED cascade onset. The generalized theory is applied to selfsustained cascades in a single focused laser pulse. According to numerical simulations, if a GeV electron bunch is used as a seed, an ordinary cascade can be converted into the selfsustained one. As an application, it would be also possible to produce this way bright collimated photon beams with up to GeV photon energies.