Laser-driven proton–boron fusion in a hollow spherical target

Laser-driven proton–boron fusion has attracted great interest both for its nature as an aneutronic reaction that produces three alpha particles and for its applications in producing short-lived medical radioisotopes. In this work, we propose a novel hollow spherical target with a rear opening to investigate proton acceleration using 2D particle-in-cell (PIC) simulations. This geometry significantly enhances laser-plasma coupling via the target normal sheath acceleration mechanism, resulting in a proton cutoff energy of 53 MeV, significantly higher than 39 MeV obtained for the flat foil target at a laser intensity of 1 × 1021 W/cm2. The strong transient electric field near the sphere opening helps in secondary acceleration of the protons, leading to higher energy and reduced divergence of protons. PIC simulations were supplemented with the Monte Carlo FLUKA simulation to study the generation of the alpha particles through proton–boron fusion in pitcher–catcher geometry. The generated alpha particle energy is around 20 MeV, and the flux is on the order of 1011/MeV. In addition, using FLUKA, we further study the production of scandium radioisotopes through interactions of protons and alpha particles with a calcium target to underscore the potential applications of this approach for medical radioisotope generation. Preliminary 3D PIC simulations were conducted to comprehensively study the proton acceleration in a hollow sphere target.