Speaker
Description
Since the initial prediction of the onset of selfsustained QED cascades upon injection of particles in certain electromagnetic field configurations [1], the pivotal theory questions remain the same: (i) What are the general conditions required to trigger such cascades? (ii) How many electron-positron pairs can be produced? (iii) What is the threshold of the phenomenon, particularly in the context of future experiments with ultra-high-intensity lasers? These questions appear to be surprisingly hard to tackle analytically beyond estimates proposed for simple field configurations (like a rotating electric field) [2, 3].
We will talk about our recent advancement in the avalanche-type cascade theory [4]. We consider the problem in a general field. While we base on familiar grounds - the kinetic approach [2] and semiclassic analysis of particle trajectories [5] within LCFA - careful treatment of these ingredients allowed us to build a new predictive model for the particle growth rates. We provide a simple formula applicable to a broad class of field configurations and robust in the full range of field strengths (e.g. $a_0$ ranging from $500$ to $10^5$). It shows excellent agreement with simulations for realistic field models that combine one or more strongly focused laser beams and can be used to identify the conditions required to generate dense electron-positron plasma.
In a general field configuration accounting for the electron and photon migration from a finite-sized strong field region appears to be crucial, in particular in the (relatively) low-field interaction regime, e.g. $a_0 < 1000$. As a consequence, a hard threshold can be derived for the cascade onset in focused laser fields. This effect was seen in simulations and not predicted by preexisting cascade models and is particularly important for planning upcoming experiments at multi-petawatt laser facilities, which will have intensity near the threshold.
[1] A. R. Bell and J. G. Kirk, PRL 101, 200403 (2008).
[2] N. V. Elkina, A. M. Fedotov, I. Y. Kostyukov, M. V. Legkov, N. B. Narozhny, PR STAB 14, 054401 (2011).
[3] T. Grismayer, M. Vranic, J. L. Martins, R. A. Fonseca, and L. O. Silva, PRE 95, 023210 (2017).
[4] A. Mercuri-Baron, A.A, Mironov, C. Riconda, A. Grassi, M. Grech, arXiv:2402.04225 (2024).
[5] A. A. Mironov, E. G. Gelfer, and A. M. Fedotov, PRA 104, 012221 (2021).
