Description
The formation of dense electron-positron pair plasmas via electromagnetic avalanche-type cascades is among the most exotic phenomena that could be observed on multi-petawatt laser systems. These cascades, characterized by exponential particle growth, require a finely tuned configuration of the electromagnetic fields where particles can be continuously accelerated and participate in nonlinear Compton scattering and Breit-Wheeler pair production.
In this talk, we will focus on the modeling of the avalanche growth rate and, in particular, the identification of the minimal physical conditions required to enter the avalanche regime. Building on our recent theoretical work [1], we present a general analytical model that captures both local cascade dynamics and the effect of particle migration out of the strong-field region. This model predicts a clear intensity threshold for avalanche onset in realistic 3D laser field configurations, contrasting the idealized uniform-field scenarios often considered. We will show how this threshold emerges in the low-field limit as a result of particle leakage from the prolific growth region, and discuss its implications for experiments aiming to generate pair plasmas at upcoming multi-petawatt laser facilities.
We will then connect these findings to our most recent work [2], in which we analyze the avalanche precursor phase expected at facilities such as NSF OPAL. Using 3D PIC simulations, we assess the feasibility of detecting early-stage avalanche dynamics in two-beam configurations with imperfect focusing and realistic seeding strategies. This offers a compelling path toward experimental validation of avalanche models and the controlled generation of relativistic pair plasmas.
References
[1] Mercuri-Baron et al., Phys. Rev. X 15, 011062 (2025)
[2] Mironov et al., arXiv:2506.02832 (2025)
