Evolution of the self-injection process in the transition of an LWFA from self-modulation to blowout regime

TL;DR

This paper investigates how the self-injection process in long wavelength infrared laser wakefield accelerators evolves from self-modulation to blowout regimes using 3D Particle-in-Cell simulations, revealing different injection mechanisms and electron behaviors.

Contribution

It provides new insights into the transition of self-injection processes between regimes in LWIR LWFA, highlighting the role of wave breaking and laser parameters.

Findings

Self-injection occurs with wave breaking in SM-LWFA but not in the blowout regime.

Wave breaking in SM-LWFA happens below the 1D wave-breaking threshold.

Electrons exhibit spatial modulations indicating direct laser acceleration.

Abstract

Long wavelength infrared (LWIR) laser driven plasma wakefield accelerators are investigated here in the self-modulated laser wakefield acceleration (SM-LWFA) and blowout regimes using 3D Particle-in-Cell simulations. The simulation results show that in SM-LWFA regime, self-injection arises with wave breaking, whereas in the blowout regime, self-injection is not observed under the simulation conditions. The wave breaking process in SM-LWFA regime occurs at a field strength that is significantly below the 1D wave-breaking threshold. This process intensifies at higher laser power and plasma density and is suppressed at low plasma densities ($\leq 1\times10^{17}$ $cm^{-3}$ here). The produced electrons show spatial modulations with a period matching that of the laser wavelength, which is a clear signature of direct laser acceleration (DLA).