Ultra-intense laser neutron generation through efficient deuteron acceleration

摘要

Experiments at the HERCULES laser facility, originally reported by C. Zulick, et al in Applied Physics Letters (2013), have produced neutron beams with energies up to 16.8(±0.3) MeV using _3~7Li(d,n)_4~8Be reactions. These efficient deuteron reactions required the selective acceleration of deuterons through the introduction of a deuter-ated plastic or cryogenically frozen D_2O layer on the surface of a thin film target. It was shown that a optimized frozen D_2O layer, formed in situ, yielded the highest efficiency deuteron acceleration with deuterons constituting over 99% of the accelerated light ions. The deuteron signal was optimized with respect to the delay between the heavy water deposition and laser pulse arrival, as well as the temperature of the target. A total conversion efficiency of laser energy to neutron energy of 1(±0.5) × 10~(-5) was obtained. The simulated neutron signal was found to be in reasonable agreement with the experimental spectra. The scattering of neutrons through shielding and target materials was investigated with MCNPX and determined to have a small effect on the observed neutron energies.