Properties of Pair Plasmas Emerging from Electromagnetic Showers in Matter

TL;DR

This paper analytically investigates electromagnetic showers in matter to understand pair plasma formation, deriving explicit spectra and conditions for pair escape and plasma creation, with implications for future laser-based experiments.

Contribution

It provides analytical solutions for pair and photon spectra in electromagnetic showers, clarifies conditions for pair escape, and proposes criteria for laboratory pair plasma generation.

Findings

Analytical expressions for photon and pair spectra in thin targets.

Conditions under which pair escape is significant.

Criteria for pair plasma formation in laboratory settings.

Abstract

Electromagnetic showers from high-energy electron beams interacting with a target are a promising path to creating pair plasmas in the laboratory. Here, we solve analytically the kinetic equations describing this process. Two regimes are defined by the ratio of the target thickness $L$ to the shower length $L_{\rm{sh}}$, which depends on the electron energy and target composition. For thin targets ($L < L_{\rm{sh}}$), we derive explicit expressions for the spectra of produced photons and pairs, as well as the number of pairs. For thick targets ($L > L_{\rm{sh}}$), we obtain the total pair number and photon spectrum. Analytical results agree well with Geant4 simulations, and it is found that significant pair escape requires $L < L_{\rm{sh}}$. The divergence, density and characteristic dimensions of the escaping pair jets are derived, and a criterion for pair plasma formation is obtained. While current laser wakefield beams are not well adapted, multi-petawatt lasers may provide new electron or photon sources suitable for laboratory pair plasma production.