High-flux neutron generation by laser-accelerated ions from single- and double-layer targets

Abstract

Contemporary ultraintense, short-pulse laser systems provide extremely compact setups for the production of high-flux neutron beams, such as those required for nondestructive probing of dense matter, research on neutron-induced damage in fusion devices or laboratory astrophysics studies. Here, by coupling particle-in-cell and Monte Carlo numerical simulations, we examine possible strategies to optimise neutron sources from ion-induced nuclear reactions using 1-PW, 20-fs-class laser systems. To improve the ion acceleration, the laser-irradiated targets are chosen to be ultrathin solid foils, either standing alone or preceded by a plasma layer of near-critical density to enhance the laser focusing. We compare the performance of these single- and double-layer targets, and determine their optimum parameters in terms of energy and angular spectra of the accelerated ions. These are then sent into a converter to generate neutrons via nuclear reactions on beryllium and lead nuclei. Overall, we identify configurations that result in neutron yields as high as sim 10^{10},{mathrm{n}},{mathrm{sr}}^{-1} in sim 1-cm-thick converters or instantaneous neutron fluxes above 10^{23},{mathrm{n}},{mathrm{cm}}^{-2},{mathrm{s}}^{-1} at the backside of lesssim 100-upmum-thick converters. Considering a realistic repetition rate of one laser shot per minute, the corresponding time-averaged neutron yields are predicted to reach values (gtrsim 10^7,{mathrm{n}} ,{mathrm{sr}}^{-1},{mathrm{s}}^{-1}) well above the current experimental record, and this even with a mere thin foil as a primary target. A further increase in the time-averaged yield up to above 10^8,{mathrm{sr}}^{-1},{mathrm{s}}^{-1} is foreseen using double-layer targets.