Efficient protons acceleration by a petawatt Laguerre-Gaussian laser from a concave micro-structured target

Laser-driven ion sources have the advantages of compact size, high density, and short bunch duration over conventional acceleration. Nevertheless, it remains challenging to simultaneously enhance the yield and quality of laser-driven ion beams for applications such as tumor therapy. Here we propose a scheme to address this challenge by using a concave micro-structured (CMS) target irradiated by multi-petawatt Laguerre-Gaussian (LG) lasers. During the interaction of the LG laser with the CMS target, a longitudinal charge-separation field with a broad dual-peak structure is excited, and it maintains this shape with a large amplitude for dozens of laser cycles. This special distribution can simultaneously accelerate and converge the ions within the laser spot region. Particle-in-cell simulations demonstrate that, under irradiation by LG lasers with peak intensities ranging from 10^20 \textW/cm^2 to 10^22 \textW/cm^2, CMS hydrocarbon targets double the high-energy proton yield compared to planar finite-sized targets while maintaining high collimation. Typically, a quasi-monoenergetic proton beam with a peak energy of \sim 72.3 MeV and a divergence angle of less than 10^\circ can be generated using the CMS target. This work could provide a reference for high-quality ion beam generation with recently available petawatt (PW)-class LG laser systems.