Neutron production from ultrashort pulse lasers using linear and circular polarization

Abstract

An implicit 2D3V particle-in-cell code is used to study proton and deuteron acceleration from an ultrathin CD foil with thickness between 20 and 200 nm using linear and circular polarization. The proton and deuteron beams drive nuclear fusion reactions from converter foils in a pitcher-catcher set-up. The neutron yield for three representative reactions d − d, d − Li, and p − Li has been calculated analytically using the total neutron production cross section and ion stopping power. For linear polarization, maximum normalized neutron yield of Y−d-d=3.4×106, Y−d-Li=3.2×107, and Y−p-Li=6.8×106 neutrons/J laser energy has been calculated at the optimum foil thickness of 50 nm. For circular polarization, the optimum foil thickness is 20 nm, for which the corresponding neutron yields are Y−d-d=1.9×106, Y−d-Li=2.0×107, and Y−p-Li=2.7×106, respectively. The laser polarization strongly affects the neutron production; for our regime, i.e., intensity I=1×1021 W/cm2, pulse duration τFWHM=30 fs, and laser energy ɛlaser=3.8 J, both the conversion efficiency of laser energy into ion kinetic energy and neutron yield are higher for linear polarization. Only for ultrathin (∼20 nm) foils in the radiation pressure acceleration regime, circular and linear polarizations yield comparable results.