The Fusion Energy Sciences office supported “A Pilot Program for Research Traineeships to Broaden and Diversify Fusion Energy Sciences” at Sandia National Laboratories during the summer of 2021. This pilot project was motivated in part by the Fusion Energy Sciences Advisory Committee report observation that “The multidisciplinary workforce needed for fusion energy and plasma science requires that the community commit to the creation and maintenance of a healthy climate of diversity, equity, and inclusion, which will benefit the community as a whole and the mission of FES”. The pilot project was designed to work with North Carolina A&T (NCAT) University and leverage SNL efforts in FES to engage underrepresented students in developing and accessing advanced material solutions for plasma facing components in fusion systems. The intent was to create an environment conducive to the development of a sense of belonging amongst participants, foster a strong sense of physics identity among the participants, and provide financial support to enable students to advance academically while earning money. The purpose of this assessment is to review what worked well and lessons that can be learned. We reviewed implementation and execution of the pilot, describe successes and areas for improvement and propose a no-cost extension of the pilot project to apply these lessons and continue engagement activities in the summer of 2022.
Mattsson, Thomas M.; Flicker, Dawn G.; Benage, John F.; Battaile, Corbett C.; Brown, Justin L.; Lane, James M.; Lim, Hojun L.; Arsenlis, Thomas A.; Barton, Nathan R.; Park, Hye-Sook P.; Swift, Damian C.; Prisbrey, Shon T.; Austin, Ryan A.; McNabb, Dennis P.; Remington, Bruce A.; Prime, Michael B.; Gray, George T.; Bronkhorst, Curt B.; Shen, Shuh-Rong S.; Luscher, D.J.L.; Scharff, Robert J.; Fensin, Sayu J.; Schraad, Mark W.; Dattelbaum, Dana M.; Brown, Staci L.
Materials in nuclear and conventional weapons can reach multi-megabar pressures and 1000s of degree temperatures on timescales ranging from microseconds to nanoseconds. Understanding the response of complex materials under these conditions is important for designing and assessing changes to nuclear weapons. In the next few decades, a major concern will be evaluating the behavior of aging materials and remanufactured components. The science to enable the program to underwrite decisions quickly and confidently on use, remanufacturing, and replacement of these materials will be critical to NNSA’s new Stockpile Responsiveness Program. Material response is also important for assessing the risks posed by adversaries or proliferants. Dynamic materials research, which refers to the use of high-speed experiments to produce extreme conditions in matter, is an important part of NNSA’s Stockpile Stewardship Program.
Mixtures of light elements with heavy elements are important in inertial confinement fusion. We explore the physics of molecular scale mixing through a validation study of equation of state (EOS) properties. Density functional theory molecular dynamics (DFT-MD) at elevated temperature and pressure is used to obtain the thermodynamic state properties of pure xenon, ethane, and various compressed mixture compositions along their principal Hugoniots. To validate these simulations, we have performed shock compression experiments using the Sandia Z-Machine. A bond tracking analysis correlates the sharp rise in the Hugoniot curve with the completion of dissociation in ethane. The DFT-based simulation results compare well with the experimental data along the principal Hugoniots and are used to provide insight into the dissociation and temperature along the Hugoniots as a function of mixture composition. Interestingly, we find that the compression ratio for complete dissociation is similar for several compositions suggesting a limiting compression for C-C bonded systems.
We use Sandia's Z machine and magnetically accelerated flyer plates to shock compress liquid krypton to 850 GPa and compare with results from density-functional theory (DFT) based simulations using the AM05 functional. We also employ quantum Monte Carlo calculations to motivate the choice of AM05. We conclude that the DFT results are sensitive to the quality of the pseudopotential in terms of scattering properties at high energy/temperature. A new Kr projector augmented wave potential was constructed with improved scattering properties which resulted in excellent agreement with the experimental results to 850 GPa and temperatures above 10 eV (110 kK). Finally, we present comparisons of our data from the Z experiments and DFT calculations to current equation of state models of krypton to determine the best model for high energy-density applications.
Hydrocarbon foams are commonly used in HEDP experiments, and are subject to shock compression from tens to hundreds of GPa. Modeling foams is challenging due to the heterogeneous character of the foam. A quantitative understanding of foams under strong dynamic compression is sought. We use Sandia's ALEGRA-MHD code to simulate 3D mesoscale models of pure poly(4-methyl-1-petene) (PMP) foams. We employ two models of the initial polymer-void structure of the foam and analyze the statistical properties of the initial and shocked states. We compare the simulations to multi-Mbar shock experiments at various initial foam densities and flyer impact velocities. Scatter in the experimental data may be a consequence of the initial foam inhomogeneity. We compare the statistical properties the simulations with the scatter in the experimental data.
Gas puff z-pinch experiments have been proposed for the refurbished Z (ZR) facility for CY2011. Previous gas puff experiments [Coverdale et. al., Phys. Plasmas 14, 056309, 2007] on pre-refurbishment Z established a world record for laboratory fusion neutron yield. New experiments would establish ZR gas puff capability for x-ray and neutron production and could surpass previous yields. We present validation of ALEGRA simulations against previous Z experiments including X-ray and neutron yield, modeling of gas puff implosion dynamics for new gas puff nozzle designs, and predictions of X-ray and neutron yields for the proposed gas puff experiments.
It has been experimentally demonstrated that deuterium gas-puff implosions at >15 MA are powerful sources of fusion neutrons. Analysis of these experiments indicates that a substantial fraction of the obtained DD fusion neutron yields {approx} 3 x 10{sup 13}, about 50%, might have been of thermonuclear origin. The goal of our study is to estimate the scaling of the thermonuclear neutron yield from deuterium gas-puff implosions with higher load currents available after the refurbishment of Z, both in the short-pulse ({approx}100 ns) and in the long-pulse ({approx}300 ns) implosion regimes. We report extensive ID and 2D radiation-hydrodynamic simulations of such implosions. The mechanisms of ion heating to the fusion temperatures of 7-10 keV are essentially the same as used in structured gas-puff loads to generate high Ar K-shell yields: shock thermalization of the implosion kinetic energy and subsequent adiabatic heating of the on-axis plasma. We investigate the role of high-atomic-number gas that can be added to the outer shell to improve both energy coupling of the imploded mass to the generator and energy transfer to the inner part of the load, due to radiative losses that make the outer shell thin. We analyze the effect of imposed axial magnetic field {approx}30-100 kG, which can contribute both to stabilization of the implosion and to Joule heating of the imploded plasma. Our estimates indicate that thermonuclear DD neutron yields approaching 10 are within the reach on refurbished Z.
We have carried out 2D simulations of three dense plasma focus (DPF) devices using the ALEGRA-HEDP code and validated the results against experiments. The three devices included two Mather-type machines described by Bernard et. al. and the Tallboy device currently in operation at NSTec in North Las Vegas. We present simulation results and compare to detailed plasma measurements for one Bernard device and to current and neutron yields for all three. We also describe a new ALEGRA capability to import data from particle-in-cell calculations of initial gas breakdown, which will allow the first ever simulations of DPF operation from the beginning of the voltage discharge to the pinch phase for arbitrary operating conditions and without assumptions about the early sheath structure. The next step in understanding DPF pinch physics must be three-dimensional modeling of conditions going into the pinch, and we have just launched our first 3D simulation of the best-diagnosed Bernard device.