Laser-driven ion acceleration in long-lived optically shaped gaseous targets enhanced by magnetic vortices

This work demonstrates high-repetition-rate laser-driven ion acceleration utilizing optically shaped gaseous targets. The optical shaping is achieved via dual, intersecting, counterpropagating laser-generated blast waves that precisely shape the underdense gas into long-lived, controlled, and reproducible near-critical density targets. The compressed target persists for several nanoseconds, time long enough to allow for the excellent synchronization between the target and the main accelerating femtosecond laser beam. Measurements of multi-MeV ion energy spectra are presented. Three-dimensional (3D) hydrodynamic simulations are used to optimize the density profile and assess the influence of the amplified spontaneous emission of the femtosecond accelerating laser pulse. A synthetic optical probing model is applied to directly compare simulations with experimental data. 3D particle-in-cell simulations reveal the formation of multi-kT, azimuthal magnetic fields, strongly suggesting magnetic vortex acceleration as the main acceleration mechanism.