Observation of early shell-dopant mix in OMEGA direct-drive implosions and comparisons with radiation-hydrodynamic simulations

Abstract

Temporally, spatially, and spectrally resolved x-ray image data from direct-drive implosions on OMEGA were interpreted with the aid of radiation-hydrodynamic simulations. Neither clean calculations nor those using a turbulent mix model can explain fully the observed migration of shell-dopant material (titanium) into the core. Shell-dopant migration was observed via time-dependent, spatially integrated spectra, and spatially and spectrally resolved x-ray images of capsule implosions and resultant dopant emissions. The titanium emission was centrally peaked in narrowband x-ray images. In post-processed clean simulations, the peak titanium emission forms in a ring in self-emission images as the capsule implodes. Post-processed simulations with mix reproduce trends in time-dependent, spatially integrated spectra, as well having centrally peaked Ti emission in synthetic multiple monochromatic imager. However, mix simulations still do not transport Ti to the core as is observed in the experiment. This suggests that phenomena in addition to the turbulent mix must be responsible for the transport of Ti. Simple diffusion estimates are unable to explain the early Ti mix into the core. Mechanisms suggested for further study are capsule surface roughness, illumination non-uniformity, and shock entrainment.

New Los Alamos Opacity Calculations

“…Although direct comparisons of our LTE opacity calculations with the NIF measurements are not appropriate, we do find that our calculated line positions appear to be consistent with the measurements presented in [12] as well as the associated modeling presented in that work. ATOMIC has been used in non-LTE mode (including consideration of spatial gradients and radiation transport) to successfully compare with earlier NIF measurements [13] and Omega measurements [14]. We finally note that the positions of the Li-like, He-like, and H-like Kr line features shown in Figure 5 appear to be in excellent agreement with the NIST recommended data for these lines [33].…”

“…Several short summaries of our new opacity tables for hydrogen through zinc have recently been published in various proceedings [10,11], and instead of repeating such summaries, we aim instead in this contribution to provide a short description of some recent work by us that attempts to calculate opacities for elements beyond zinc. Such extensions are motivated by the continuing importance of accurate opacities and radiation transport models to other plasma studies found in inertial confinement fusion (ICF) research (e.g., [12][13][14]), industrial plasmas [15], and in the field of magnetic confinement fusion. Some of these fields require models for elements that are not normally important in astrophysics research (such as Sn or W), and it is important to be able to provide accurate opacities for such systems.…”

Multiple-view spectrally resolved x-ray imaging observations of polar-direct-drive implosions on OMEGA

“…To compare with the PDD implosion observations, Fig. 7 shows an image recorded in OMEGA shot 65036 where similar targets were driven with a spherically symmetric, 60-beam drive [31]. No "double-bun" structure was observed in these experiment along any LOS.…”

Properties of hot-spot emission in a warm plastic-shell implosion on the OMEGA laser system

“…In an unstable implosion, a trace amount of shell material mixed into the hot spot can increase the x-ray emission measurably because of the relatively high emissivity per atom of carbon (or other shell materials) without significantly altering the DT concentration and the hot-spot conditions [14]. Consequently, measured hot-spot conditions and mixing mass were measured in both NIF and OMEGA implosions, based on the K-shell line emission of M-shell ionization species of higher-Z shell dopants [15][16][17]. Dopant line emission indicates mix originating from the doped shell layers only, while carbon continuum emission indicates fuel-shell mix originating from anywhere in the capsule shell.…”