Efficient Simulation of Electron-Positron Pair Production in Foam Targets in the low χ-Regime

TL;DR

The work addresses efficient simulation of strong-field QED–driven electron-positron pair production in foam-cone targets under ultra-intense laser fields. It introduces a subsampling routine for PIC code vlpl to decouple the granularity of photon emission and pair creation from macroparticle weights, preserving the correct statistics via binomial sampling. By applying 2D/3D simulations with a high-intensity laser ($1.5\ \mathrm{kJ}$, $a_0\sim194$) interacting with a near-critical foam and a cone target, the authors report large yields of pairs ($\sim10^{11}$) and show that subsampling dramatically improves the positron-energy spectrum resolution—from about $~10^3$ macroparticles to $~10^6$ while maintaining total yields. The key contribution is a practical, low-cost method to model SF-QED processes in PIC simulations and enable scalable exploration of pair cascades in realistic target geometries.

Abstract

The generation of electron-positron pairs using direct laser-accelerated electrons and a cone-shaped reflector target for the generation of strong electromagnetic fields is investigated using particle-in-cell simulations. A newly implemented sub-sampling routine for the code vlpl is presented which allows for a better description of quantum electrodynamical processes which would otherwise come at a high computational cost.

Figures (3)

• Figure 1: Depiction of the setup in PIC simulations. (a) The laser (red/blue) propagates through the homogenized foam (grey), accelerating electrons via DLA. (b) The laser pulse is reflected at the cone target (black) and high-energy photons (green) are produced. (c) The photons subsequently decay into electron-positron pairs (orange).
• Figure 2: Schematics for the implementation of a process $P$ (a) without sub-sampling and with sub-sampling (b).
• Figure 3: Energy spectrum of the produced Breit-Wheeler pairs with and without subsampling.