Numerical investigation of laser-driven proton bunching with multi-species CH targets using high-energy, long-pulse lasers

This paper reports a numerical study based on previously published experiments with high-power laser systems, in which high-energy bunches were observed in proton spectra. In these experiments, thin targets were irradiated with hundreds of joules and pulse durations of several hundred femtoseconds. We carried out a simulation campaign combining hydrodynamic and particle-in-cell codes to analyze the origin of the proton energy bunch. The study demonstrates how laser parameters, target thickness, and ionization dynamics influence proton bunch formation. Possible acceleration mechanisms were explored, and the role of a Coulomb piston of highly ionized carbon ions in shaping the proton spectrum within the target normal sheath acceleration regime is demonstrated.