Investigation of the yield degradation of the first shaped-pulse implosion experiments on the SG-III laser facility

Abstract

The first shaped-pulse inertial confinement fusion implosion experiments of the deuterium-deuterium (DD) gas-filled plastic (CH) capsules have been done at the SG-III laser facility [He and Zhang, Eur. Phys. J. D 44, 227 (2007); Zheng et al., Matter Radiat. Extremes 2, 243 (2017)]. The measured neutron yield is much lower than that predicted by one-dimensional (1D) simulations, and as the trough duration of the drive source increases, the neutron yield over clean decreases rapidly to less than 1%. To understand the primary reason for this decrease in yield, we numerically simulated the capsule implosion to investigate the effects of the support tent and the various capsule-surface defects on the implosion performance. The validity of the underlying 1D model is supported by the agreement between the results of the 1D simulation and experimental data for the implosion trajectory and fuel areal density. Compared with square-pulse implosions, shaped-pulse implosions exhibit a much larger growth in hydrodynamic instabilities. The numerical neutron yields of the shaped-pulse implosions are much more sensitive to perturbations seeded by inward-facing divots on the outer ablator surface. Yield degradation is mainly caused by a reduction in mechanical power exerted by the distorted shell on the central DD gas, which significantly lowers the fuel temperature and pressure.