Predominant Contribution of Direct Laser Acceleration to High-Energy Electron Spectra in a Low-Density Self-Modulated Laser Wakefield Accelerator

Abstract

The two-temperature relativistic electron spectrum from a low-density ($3\times 10^{17}$~cm${}^{-3}$) self-modulated laser wakefield accelerator (SM-LWFA) is observed to transition between temperatures of $19\pm 0.65$ and $46\pm 2.45$ MeV at an electron energy of about 100 MeV. When the electrons are dispersed orthogonally to the laser polarization, their spectrum above 60 MeV shows a forking structure characteristic of direct laser acceleration (DLA). Both the two-temperature distribution and the forking structure are reproduced in a quasi-3D \textsc{Osiris} simulation of the interaction of the 1-ps, moderate-amplitude ($a_0=2.7$) laser pulse with the low-density plasma. Particle tracking shows that while the SM-LWFA mechanism dominates below 40 MeV, the highest-energy ($>60$ MeV) electrons gain most of their energy through DLA. By separating the simulated electric fields into modes, the DLA-dominated electrons are shown to lose significant energy to the longitudinal laser field from the tight focusing geometry, resulting in a more accurate measure of net DLA energy gain than previously possible.

References in corpus (5)

• Generating multi-GeV electron bunches using single stage laser wakefield acceleration in a 3D nonlinear regime
• Femtosecond x rays from laser-plasma accelerators
• Synergistic Laser Wakefield/Direct Laser Acceleration in the Plasma Bubble Regime
• Implementation of a hybrid particle code with a PIC description in r-z and a gridless description in $\varphi$ into OSIRIS
• Role of direct laser acceleration in energy gained by electrons in a laser wakefield accelerator with ionization injection

Cited by in corpus (5)

• Direct laser acceleration in underdense plasmas with multi-PW lasers: a path to high-charge, GeV-class electron bunches
• Direct laser acceleration: A model for the electron injection from the walls of a cylindrical guiding structure
• Direct laser acceleration in varying plasma density profiles
• Accurate simulation of direct laser acceleration in a laser wakefield accelerator
• GeV-scale accelerators driven by plasma-modulated pulses from kilohertz lasers