High-density electron–ion bunch formation and multi-GeV positron production via radiative trapping in extreme-intensity laser–plasma interactions

Abstract

Multi-petawatt laser systems will open up a novel interaction regime mixing collective plasma and quantum electrodynamic processes, giving rise to prolific generation of gamma-ray photons and electron–positron pairs. Here, using particle-in-cell simulations, we investigate the physics of the interaction of a 10 ^24 W cm ^−2 intensity, 30 fs duration, circularly polarized laser pulse with a long deuterium plasma at classically overcritical electron density (10 ^22 cm ^−3 ). We show that radiative trapping of the plasma electrons causes a high-density (∼5 × 10 ^23 cm ^−3 ), quasineutral electron–ion bunch to form inside the laser pulse. This phenomenon is accompanied by up to ∼40% energy conversion efficiency of the laser into gamma rays. Moreover, we find that both the radiation-modified Laplace force and the longitudinal electric field exerted on the positrons created by the multiphoton Breit–Wheeler process can accelerate them to GeV-range energies. We develop a theoretical model, the predictions of which provide a good match to the simulation results. Finally, we address the influence of the ion mass, showing that the laser absorption and positron acceleration is enhanced with deuterons compared to protons.

Keywords

• radiation reaction
• ultraintense laser-solid interactions
• synchrotron radiation
• multiphoton Breit–Wheeler process
• nonlinear inverse Compton scattering