Description
The interaction of a high-intensity laser pulse with a near-critical plasma target can lead to the generation of electron beams via direct laser acceleration (DLA) in a plasma channel [1]. This mechanism yields electron beams that are relatively collimated (divergence ~0.1 rad), with charge in the tens of nC, (up to μC [2]) and an exponential energy spectrum with ‘temperatures’ in the tens of MeV. These electron beams are drastically different from the ones obtained by laser wakefield acceleration (LWFA) and are uniquely suited for applications requiring high particle fluxes, such as neutron generation, nuclear physics studies and industrial imaging.
While electron acceleration dynamics in DLA have been well-studied analytically and in particle-in-cell (PIC) simulations [3,4], the spin dynamics of electrons in this regime have remained largely unexplored. In this work, we analytically investigate electron spin dynamics in DLA based on the Thomas-Bargmann-Michel-Telegdi (T-BMT) equation. We demonstrate that for the most energetic, planar electron trajectories, the spin projection perpendicular to the plane of motion remains conserved. Furthermore, we show that under the ultra-relativistic assumption (γ≫1) the net spin precession averaged over a single betatron oscillation period is negligible, i.e., spin averaged over a betatron oscillation period is conserved. These findings are corroborated by the test particle simulations and 3D EPOCH PIC simulations. Finally, we address the practical feasibility of generating and preserving spin-polarized electron beams in realistic DLA experimental scenarios.
This work is funded by EPSRC grant number EP/V049461/1, EP/Y01751X/1 and ELI/ERIC.
[1] Pukhov, A., Sheng, Z. M. & Meyer-ter-Vehn, J. Phys. Plasmas 6, 2847–2854 (1999).
[2] Rosmej, O. N., et al. Plasma Phys. Controlled Fusion 62, 115024 (2020).
[3] Gahn, C., et al. Phys. Rev. Lett. 83, 4772–4775 (1999).
[4] Arefiev, A. V., et al. Physics of Plasmas 23.5 (2016).