Efficient ion acceleration driven by a Laguerre–Gaussian laser in near-critical-density plasma

Laser-driven ion accelerators have the advantages of compact size, high density, and short bunch duration over conventional accelerators. Nevertheless, it is still challenging to generate ion beams with quasi-monoenergetic peak and low divergence in experiments with the current ultrahigh intensity laser and thin target technologies. Here we propose a scheme that a Laguerre–Gaussian laser irradiates a near-critical-density (NCD) plasma to generate a quasi-monoenergetic and low-divergence proton beam. The Laguerre–Gaussian laser pulse in an NCD plasma excites a moving longitudinal electrostatic field with a large amplitude, and it maintains the inward bowl-shape for dozens of laser durations. This special distribution of the longitudinal electrostatic field can simultaneously accelerate and converge the protons. Our particle-in-cell (PIC) simulation shows that the efficient proton acceleration can be realized with the Laguerre–Gaussian laser intensity ranging from 3.9 × 10²¹ W⋅cm⁻²–1.6 × 10²² W⋅cm⁻² available in the near future, e.g., a quasi-monoenergetic proton beam with peak energy ∼ 115 MeV and divergence angles less than 5° can be generated by a 5.3 × 10²¹ W⋅cm⁻² pulse. This work could provide a reference for the high-quality ion beam generation with PWclass laser systems available recently.