Enhanced proton–boron fusion yield with advanced target geometries under direct laser illumination

Laser-driven fusion reactions for the development of bright particle sources or the production of short-lived isotopes remain an active research theme. We propose a comprehensive analysis and a fast modeling approach to highlight optimization strategies on the fusion yields stemming from advanced target designs. Particle-in-cell simulations were supplemented with an inline Monte Carlo approach to evaluate the proton–boron fusion events under direct laser illumination for planar and spherical target geometries. The time evolution and the spatial localization of the nuclear reactions are systematically compared to reveal a multi-phase mechanism in the folded geometries. For both architectures, a shared initial phase of fusion occurs in the laser spot vicinity, following from ions accelerated by the laser radiation pressure forward into the target. Meanwhile, the circulation of hot electrons issued from the laser-plasma interaction leads to the development of sheath fields along the target walls. In a closed geometry, the corresponding accelerated ions may be directed toward dense parts of the target, significantly increasing the number of created α-particles. We analyze the energy distribution of the ion populations issued from the different acceleration mechanisms and assess the corresponding efficiencies in the fusion processes. The use of a double cavity allows for further exploitation of the sheath field acceleration, raising the α yield almost an order of magnitude higher than for the planar case.