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Hoffman, Nelson M.

Publications and source records attributed to Hoffman, Nelson M..

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Implosion simulations and optimum times of radiographic Images in OMEGA high-density-carbon cylinder experiments

The Los Alamos Ignition Threshold team is planning direct-drive cylinder implosion experiments (CylDRT24B) at the OMEGA laser, scheduled for Thursday 23 May 2024, to investigate the effect of granular microstructure in high density carbon (HDC) shells. Granular microstructure is believed to play a crucial role in seeding perturbations, reducing compression, and enhancing mix in the implosion of HDC shells at the National Ignition Facility (NIF). But the ICF community lacks a detailed understanding of how grains induce these effects, owing partly to the practical difficulty of numerically simulating the behavior of tiny nanometer-scale granular structures in laboratory-scale experiments. Our planned experiments are aimed at acquiring data to help constrain simulations and calibrate reduced models.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Use of tritium-rich fuel to improve the yield of layered deuterium/tritium inertial fusion capsules

In deuterium–tritium (DT) ice layered implosions, nearly all hot spot mass at peak burn comes from the dense fuel. Accurate prediction of the fuel mass ablation, including the enthalpy associated with mass inflow into the hot spot from the dense fuel, is essential to understanding the energetics and ignition of the hot spot in layered implosions. A recently published boundary layer analysis (Daughton et al., 2023) indicates a faster mass ablation rate than in previous analyses of layered implosions. Inclusion of this effect provides a better match to simulations and leads to a new ignition threshold where the temperature of the dense fuel plays a critical role. This analysis motivates possible new directions for improved capsule performance. Here, the authors present evidence in support of one such approach: the use of tritium-rich ice to decrease 14 MeV neutron scattering and heating of the dense fuel, resulting in less mass ablation and more robust burn of the hot spot. It is found from numerical simulations that despite a less favorable D:T ratio in the ice, the use of a 40:60 D:T ratio leads to an increase in capsule yield of 17% percent compared with that of a 50:50 D:T ratio fuel for capsules resembling those of the recent N210808 ignition experiment on the NIF (Abu-Shawareb et al., 2022) and an increase of 74% compared with that of a 60:40 D:T ratio fuel capsule. Finally, these results are potentially important for modeling all layered implosions, since some degree of DT fractionization may arise naturally during the beta layering process. In addition, this physics is important for the feasibility of high-gain capsule designs that seek to minimize tritium usage, as in some inertial fusion energy concepts.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Target Design for XFEL Experiments

High-energy-density (HED) experiments utilizing X-ray free electron lasers (XFELs) must take a different approach to fielding these experiments than the current methodology used for the large HED facilities in the United States. The XFELs and their associated laser drivers have a much faster repetition rate than do the larger facilities. Experiments must be designed to execute hundreds rather than a few shots per experimental run. The new paradigm requires a different approach to data collection and analysis. It also requires an integrated approach to experiment and target design. Here, in this study, we developed new target designs for a future XFEL experiment that meet both experiment and cost goals.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗