Multi-GeV Electron Acceleration in Helium using Novel Injection Mechanisms and a Custom Density Profile

Bessel-beam induced channels over meter-scale gas jets have enabled 10 GeV, multi-Joule self-waveguided laser wakefield acceleration (LWFA) [1,2] and are a promising approach for next-generation experiments surpassing 10 GeV. However, single-stage, mono-energetic LWFA beyond 10 GeV likely requires controlled injection schemes at low densities with tapered waveguides to optimize energy gain. We present the successful implementation of self-waveguided LWFA at ELI Beamlines, utilizing the L3 laser system delivering 13 J, 30 fs pulses at 0.2 Hz and a 20 cm channel over a helium gas jet [3]. In these experiments, the channel-forming beam was split post-compression and formed with an off-axis reflective axicon. We present results including two novel injection mechanisms utilizing (1) local optical modification of the channel and (2) a local nanoparticle source, each capable of scaling to accelerator densities to < 10¹⁷ cm³ on axis.