Towards the Optimisation of Direct Laser Acceleration

TL;DR

This paper reports experimental and simulation evidence of direct laser acceleration (DLA) of electrons to over 500 MeV using a high-energy laser pulse in a low-density plasma, highlighting the role of self-generated magnetic fields.

Contribution

It demonstrates successful electron acceleration via DLA at high energies and explores the influence of self-generated magnetic fields on electron dynamics.

Findings

Electrons reached energies of 505 MeV with high charge.

Simulation results show similar energy trends with plasma density.

Self-generated magnetic fields significantly affect electron motion.

Abstract

Experimental measurements using the OMEGA EP laser facility demonstrated direct laser acceleration (DLA) of electron beams to (505 $\pm$ 75) MeV with (140 $\pm$ 30)~nC of charge from a low-density plasma target using a 400 J, picosecond duration pulse. Similar trends of electron energy with target density are also observed in self-consistent two-dimensional particle-in-cell simulations. The intensity of the laser pulse is sufficiently large that the electrons are rapidly expelled from along the laser pulse propagation axis to form a channel. The dominant acceleration mechanism is confirmed to be DLA and the effect of quasi-static channel fields on energetic electron dynamics is examined. A strong channel magnetic field, self-generated by the accelerated electrons, is found to play a comparable role to the transverse electric channel field in defining the boundary of electron motion.