2D hydrodynamic simulations of generation of high-current proton beams by relativistic skin-layer laser-plasma interaction

Abstract

The properties of fast proton beam generation by skin-layer ponderomotive acceleration (SLPA) induced by a short (< 1 ps) laser pulse are studied using 2D two-fluid relativistic code. It is found that both for subrelativistic and relativistic laser intensities, the crucial parameter determining the spatial structure and angular divergence (Θ _b) of the proton beam is the ratio d _L/L _n, where d _L is the laser beam diameter and L _n is the density gradient scale length of preplasma in front of the target. When this ratio is relatively small (< 10), the proton beam generated at relativistic laser intensities has a bubble-like structure and Θ is large. When d _L is at least tens times greater than L _n, the transverse distribution of the proton density and the proton current density in the beam follow the spatial shape of the laser beam and Θ _b is small. In the last case, highly collimated high-current (MA) proton beams can be produced by SLPA at relativistic laser intensities.