Laser-Driven Collimated Neutron Sources Based on Kinematic Focusing

Abstract

Neutron beams are unique tools to probe samples in many fields, such as biology medicine and fusion research. Access to such sources is traditionally limited to large particle accelerators. However, laser-driven pulsed neutron sources have attracted attention in recent years due to their compactness and cost savings. Although, in practical applications, the major obstacle is terribly low neutron flux due to the isotropic scattering. Here we propose a roadmap for laser-driven neutron sources based on ``kinematic focusing,'' which is ideal for producing highly collimated neutron beams and leads to the neutron-flux enhancement by more than 1 order of magnitude. Such a good collimation is conducive to the detection of samples located several meters from neutron sources, and it becomes feasible to place sensitive detectors adjacent to the neutron sources without the necessity of heavy shielding. A theoretical model for kinematic focusing and supporting two-dimensional particle-in-cell simulations are presented. It is shown that a well-collimated neutron beam, with the maximal divergence angle of about ${30}^{\ensuremath{\circ}}$, is generated by bombardment of a hydrogen target with ${\mathrm{Li}}^{3+}$ beams, which come from a metallic lithium foil irradiated by a short laser pulse at an intensity of $5.5\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{0.2em}{0ex}}\mathrm{W}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. This proposed method can be achieved by present-day petawatt laser facilities.