Dynamics of high-energy proton beam acceleration and focusing from hemisphere-cone targets by high-intensity lasers

摘要

Acceleration and focusing of high-energy proton beams from fast-ignition (FI) -related hemisphere-conenassembled targets have been numerically studied by hybrid particle-in-cell simulations and compared with thosenfrom planar-foil and open-hemisphere targets. The whole physical process including the laser-plasma interactionnhas been self-consistently modeled for 15 ps, at which time the protons reach asymptotic motion. It is found thatnthe achievable focus of proton beams is limited by the thermal pressure gradients in the co-moving hot electrons,nwhich induce a transverse defocusing electric field that bends proton trajectories near the axis. For the advancednhemisphere-cone target, the flow of hot electrons along the cone wall induces a local transverse focusing sheathnfield, resulting in a clear enhancement in proton focusing; however, it leads to a significant loss of longitudinalnsheath potential, reducing the total conversion efficiency from laser to protons.