Predominant contribution of direct laser acceleration to high-energy electron spectra in a low-density self-modulated laser wakefield accelerator

oleh: P. M. King, K. Miller, N. Lemos, J. L. Shaw, B. F. Kraus, M. Thibodeau, B. M. Hegelich, J. Hinojosa, P. Michel, C. Joshi, K. A. Marsh, W. Mori, A. Pak, A. G. R. Thomas, F. Albert

Format: Article
Diterbitkan: American Physical Society 2021-01-01

Deskripsi

The two-temperature relativistic electron spectrum from a low-density (3×10^{17}  cm^{-3}) self-modulated laser wakefield accelerator (SM-LWFA) is observed to transition between temperatures of 19±0.65 and 46±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 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.