Onset of electron-seeded cascades in generic electromagnetic fields

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.

Opacity of relativistically underdense plasmas for extremely intense laser pulses

“…However, avalanche-like QED cascades do not develop in ordinary plane-wave geometry and need quite dense plasma to develop in the sum of the incident and the reflected field, or to develop on the plasma-vacuum interface without reflection [17]. Alternatively, noticeable transverse field gradient is needed for cascade development in the field of a single laser pulse [18].…”