Description
Laser wakefield acceleration (LWFA) is a promising method for realizing compact high-energy electron accelerators. This mechanism uses plasma waves generated via the interaction of intense ultrashort laser pulses with gas targets to accelerate electrons to relativistic velocities. The plasma medium can sustain electric fields up to 100 GV/m - three orders of magnitude higher than conventional particle accelerators - thus allowing significant reductions in accelerator size and cost.
Although LWFA has demonstrated multi-GeV energies, stable and reproducible electron beams with narrow energy spreads and high charges remain challenging to achieve. Reaching multi-GeV electron energies with existing PW and multi-PW lasers requires long acceleration lengths and low-density plasmas (10¹⁶-10¹⁷ cm⁻³). Under these conditions, extended laser guiding becomes essential, creating two critical challenges: maintaining stable waveguides over long distances and achieving controlled electron injection in preformed plasma channels.
Bessel beam-generated plasma channels address the first challenge by providing stable laser guiding over extended distances. Unlike Gaussian beams, the Bessel beam transverse profile is invariant over its depth of focus and can create deep, smooth plasma channels with well-defined density profiles. These channels provide stable waveguides for the main laser pulse, enabling long-distance acceleration while maintaining beam quality.
However, the second challenge remains: most proven injection schemes, such as density tailoring or optical injection, are hard to implement in preformed plasma channels. We investigate nanoparticle-triggered electron injection as a solution [1]. In this approach, a nanoparticle contained in the gas target is ionized by the laser pulse, creating a strong electric field that attracts and injects electrons both from the surrounding plasma and from the nanoparticle itself. This enables controlled electron injection even at the reduced plasma densities required for multi-GeV acceleration.
This contribution aims to explore this injection scheme using quasi-3D and 3D PIC simulations. We also present preliminary experimental results from the ELBA platform at ELI Beamlines on nanoparticle-assisted injection in Bessel beam-generated plasma channels, achieving stable electron beam generation with high charge, and low energy spread.
[1] A. Špádová, et al.; Toward controlling electron beam charge with nanoparticle-assisted laser wakefield accelerators. Phys. Plasmas 1 December 2025; 32 (12): 123104. https://doi.org/10.1063/5.0295050