Injection dynamics of direct-laser accelerated electrons in a relativistic transparency regime

TL;DR

This paper investigates how electron injection occurs in direct laser acceleration within relativistically transparent plasmas, revealing the roles of ion waves and magnetic fields through simulations and analysis.

Contribution

It introduces a detailed understanding of electron injection mechanisms in DLA regimes, highlighting the influence of ion waves and magnetic fields, which was previously not well understood.

Findings

Ion waves modulate electric fields to guide electrons to the acceleration region

Self-generated magnetic fields can suppress electron injection

Insights enable optimization of laser-driven electron and photon sources

Abstract

The dynamics of electron injection in the direct laser acceleration (DLA) regime was investigated by means of three-dimensional particle-in-cell simulations and theoretical analysis. It is shown that when an ultra-intense laser pulse propagates into a near-critical density or relativistically transparent plasma, the longitudinal charge-separation electric field excites an ion wave. The ion wave modulates the local electric field and acts as a set of potential wells to guide the electrons, located on the edge of the plasma channel, to the central region, where the DLA takes place later on. In addition, it is pointed out that the self-generated azimuthal magnetic fields tend to suppress the injection process of electrons by deflecting them away from the laser field region. Understanding these physical processes paves the way for further optimizing the properties of direct-laser accelerated electron beams and the associated X/gamma-ray sources.