Direct-drive is one of the key approaches in the study of inertial confinement fusion, but the laser imprinting caused by laser intensity inhomogeneities is one of the main obstacles to achieving ignition in direct-drive. It has previously been demonstrated that a thin high-Z overcoat on the laser side of the target can significantly mitigate laser imprinting (S P Obenschain et al 2002 Phys. Plasmas9 2234). In the current work, the 1D multi-group radiation hydrodynamic code RDMG, coupled with the detailed configuration accounting non-LTE atomic physics package MBDCA (RDMG−MBDCA) was used to study a Au-coated ignition target and its implosion performances under laser direct-drive, and a bare CH target was also simulated for comparison. Our study shows that the shell compressibility in the Au-coated target is enhanced with a smaller in-flight adiabat αif and a higher neutron yield Yid than in the bare CH target. This is because the Au coating helps to maintain a hotter CH plasma, which can ablate a wider electron conduction region with lower density leading to a weaker second shock, creating a more compressed shell and a higher yield than the bare CH target. We also compared the simulations from RDMG−MBDCA with those from RDMG−AA which is coupled with an averaged-atom (AA) non-LTE model. As a result, the shell from the AA model is less compressed with a higher αif and a lower Yid because the AA model gives a higher inward x-ray emission during the pre-pulse than the DCA model does, which therefore drives a stronger shock and leads to a higher fuel entropy.
Fusion energy with lasers, direct drive targets, and dry wall chambers