LLE Review 149

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Highlights

This volume of the LLE Review, covering October–December 2016, features “Three-Dimensional Hydrodynamic Simulations of OMEGA Implosions,” which considers the effects of low-mode asymmetries on OMEGA direct-drive implosions in the three-dimensional Eulerian hydrodynamic code ASTER. Beam-power imbalance, beam mispointing, beam mistiming, target offset, and variation in target-layer thickness are considered using values determined from experimental measurements. ASTER indicates that implosion performance is affected mainly by target offset (~10 to 20 µm), beam-power imbalance (σ_rms ~ 10%), and variation in target-layer thickness (~5%).

Additional highlights of research presented in this issue include the following:

• Calculations of the equation of state of silicon using density-functional-theory molecular-dynamics for densities from 0.001 to 500 g/cm³ and temperatures from 2000 to 108 K are reported. This first-principles equation of state (FPEOS) is compared to SESAME 3810. The Hugoniot from FPEOS is ~20% softer than that from SESAME 3810. For off-Hugoniot conditions, the pressure and internal energy from FPEOS are higher than SESAME 3810 below 10⁴ to 10⁵ K, depending on density, and lower at higher temperatures. In LILAC simulations of the implosion of a silicon shell, FPEOS gives ~30% higher areal density and ~70% higher neutron yield than SESAME 3810, because of the larger compressibility of silicon in FPEOS.
• Analysis of measurements of the deuterium–tritium (DT) to deuterium–deuterium (DD) neutron yield ratio from cryogenic target experiments on OMEGA indicates no effect of species separation in these experiments.
• Results from OMEGA experiments on spherically converging shocks, comparing CH, Be, C, and SiO₂ ablators. CH gives 2 to 3× more hot electrons than any other ablator and a higher effective ablation pressure, which is attributed to stronger damping of ion-acoustic waves by H ions.
• Results from backlighting of cryogenic target experiments on OMEGA using Si He_α emission driven by OMEGA EP are reported. The imaging system has been used to study the evolution of nonuniform ablators, perturbations caused by mounting stalks, and carbon mix into the DT. Mix has only been observed for adiabats below 4.
• A description is given of a new technique to extract electron density profiles from angular filter refractometry (AFR) measurements using a simulated annealing algorithm. A seven-parameter function is chosen for the electron density and used to generate an AFR image that is compared to the measurement using a χ² test. The algorithm was applied to measurements of plasma expansion from a plane target and produced a fit with a statistical uncertainty of no more than 10% in the region of interest.