Performance of Longitudinal Direct Acceleration in particle-in-cell simulations with realistic laser and hollow target parameters

Longitudinal Direct Acceleration (LDA) is a laser-driven mechanism that exploits the longitudinal electric field of an ultraintense laser to accelerate electrons in microstructured targets. When a laser pulse propagates through a hollow microchannel, electrons ‘surf’ along the walls with the laser longitudinal field, gaining energy efficiently over extended distances [1]. Using three-dimensional particle-in-cell simulations with parameters representative of the ELI-NP facility, we study LDA in hollow targets with 15 μm inner diameter and 200 μm length, irradiated by a laser with a0=28. We find that electrons are accelerated to 350 MeV with an angular spread below 5°. This energy is comparable to traditional transverse-field driven Direct Laser Acceleration (DLA) but with much better collimation. We also find that while a 5° laser misalignment reduces electron energy gain and beam collimation, it significantly enhances gamma-ray emission - increasing the fraction of laser energy converted to photons with energies greater than 100keV from 10^-6 to 10^-4. These results convey that even with realistic target fabrication parameters and laser alignment challenges, LDA is a strong candidate for electron acceleration and gamma radiation.

[1] Z. Gong et al., Plasma Phys.and Control. Fusion 61(3), 035012 (2019).