Plastic ablator ignition capsule design for the National Ignition Facility

Abstract

The National Ignition Campaign, tasked with designing and fielding targets for fusion ignition experiments on the National Ignition Facility (NIF), has carried forward three complementary target designs for the past several years: a beryllium ablator design, a plastic ablator design, and a highdensity carbon or synthetic diamond design. This paper describes current simulations and design optimization to develop the plastic ablator capsule design as a candidate for the first ignition attempt on NIF. The trade-offs in capsule scale and laser energy that must be made to achieve a comparable ignition probability to that with beryllium are emphasized. Large numbers of 1-D simulations, meant to assess the statistical behavior of the target design, as well as 2-D simulations to assess the target's susceptibility to Rayleigh-Taylor growth are presented.

Multiphase equation of state for carbon addressing high pressures and temperatures

“…This is the SLOW decay model, with ν = 1/3 in Eqs. (8) and (10). (b) The DFT average-atom model [30] for C, which we denote AA-DFT, is used for F elec .…”

“…These studies were conducted with density functional theory (DFT) molecular dynamics (MD). Much of this recent focus on the carbon EOS, specifically in states of compression reached when starting in the diamond phase, has arisen from the interest of using high-density carbon as an ablator material for capsules designed to achieve fusion at the National Ignition Facility [10]. While these experimental and theoretical studies have been useful in constraining the EOS of carbon for this and related applications, it is crucial to note that the states reached by the ablator in inertial confinement fusion (ICF) are expected to include temperatures in excess of tens of eV [10].…”

Improved Performance of High Areal Density Indirect Drive Implosions at the National Ignition Facility using a Four-Shock Adiabat Shaped Drive

“…However, increased dopant concentration also steepens the ablation front density gradient leading to more ablation front growth. The graded dopant configuration is designed to optimize these trade-offs [43]. Simulations predict that 2 × Si is more stable to interface growth while more unstable to ablation front growth.…”

Capsule modeling of high foot implosion experiments on the National Ignition Facility

“…In progressing from N130812 to N140819, the maximum ablation front growth factor more than doubles from ∼170 to ∼430. Also evident in these spectra is the importance of the ablative Richtmyer-Meshkov (RM) oscillation [25] in setting the node in the growth factor spectrum [22,23,[26][27][28][29][30]: as the ablator was thinned in N140520 and N140819, and the pulse length consequently shortened, the time for this RM oscillation was reduced and the location of the growth factor node moved froml 80 to ∼120, resulting in enhanced growth of shorter wavelength features. Figure 2 plots the maximum of each growth factor spectrum from figure 1 versus simulated peak implosion velocity.…”

“…As shown in figure 1, the linear stability of these implosions is quantified by comparing their ablation front growth factors. These growth factors are defined as the ratio of the perturbation amplitude at the time of peak implosion velocity relative to the initial perturbation amplitude for an individual Legendre mode [21][22][23]. For all cases, the simulations were run using a 2D wedge initialized with a small Gaussian bump (15 μm wide by 1 nm in height) on the ablator surface at the axis of symmetry.…”