Beam shape effect on enhanced laser wakefield acceleration of electrons driven by 10-fs mJ-class pulses.

Laser wakefield acceleration (LWFA) of electrons was investigated using quasi-3D Fourier–Bessel Particle-In-Cell (FBPIC) simulations to optimise the interplay between laser beam structure and plasma target parameters. Gaussian (G) and Bessel–Gauss (BG) beams driven by a 40 mJ, 10 fs laser pulse were compared, representing few-cycle mJ-class (10–100 mJ) laser systems, across a range of the normalised vector potentials a0 = 1.75–5.6. The results show that, for a fixed laser system with 40 mJ pulse energy and 10 fs duration, BG beams extend the effective acceleration length and improve electron energy gain by 20–27% relative to G drivers, despite variations in 0 arising from different focal geometries. The extended focal zone of BG beams mitigates diffraction losses, while ionisation injection from a 1% nitrogen admixture produces stable injection over a distance of ~ 100 μm at a0​=2.0. However, laser pulse evolution leads to an intensity drop by a factor of 2–2.5 over 300–500 μm, ultimately limiting the maximum acceleration length. These findings confirm that BG beams offer a robust pathway to enhance LWFA performance at sub-100 mJ laser energies, with direct implications for compact high-repetition-rate plasma accelerators.