Livermore scientists at the National Ignition Facility (NIF) have gained new insights into the after-effects of a supernova explosion. The results of their research, which were published in the April 19, 2018, edition of Nature Communications, could play a role in how inertial confinement fusion and high-energy-density science experiments are conducted at the Laboratory.
When a supernova explodes, it creates an enormous shock wave with high energy flux (heat and radiation) that penetrates into the surrounding medium. When the shock reaches the end of the medium, it forms a reverse shock that runs back into the expanding ejecta material and piles up the ejecta in the high-density mass. This interface between the low-density, heated surrounding medium and the high-density mass, pressured by the shock wave, creates Rayleigh–Taylor (RT) hydrodynamic instabilities. RT instabilities play an important role in a supernova as they can change the dynamics of heavy-elements transfer from the supernova core to the surrounding medium. Similar phenomenon can occur during fusion experiments at NIF, where RT hydrodynamic instabilities can cause too much target capsule material to mix with the fuel, impeding the fusion reaction.
In the study, Laboratory physicists Hye-Sook Park and Channing Huntington, along with international researchers and colleagues at the University of Michigan, used NIF to generate high-energy radiation fluxes to determine whether the fluxes had an effect on growth of RT instabilities. The team ultimately found that the amount of heat generated by high-energy fluxes lessens mixing of the materials and therefore could reduce the growth of RT instabilities in supernova remnants. Based on their findings, Park and the research team are now ready to conduct further tests. “We can be creative about how we produce heat fluxes using the NIF laser to more closely mimic astrophysical conditions,” says Park. “Many avenues of opportunity are open to explore.”
Contact: Hye-Sook Park (925) 422-7062 (park1@llnl.gov).
Using high-powered laser beams, scientists from Lawrence Livermore, Johns Hopkins University, Princeton University, and the University of Rochester have compressed iron–silicon alloys to unprecedented pressures—matching those found in the center of planets the size of three Earth masses. The measurements of the crystal structure and density of the compressed alloys have provided potential details about the interior makeup of other Earthlike planets. The research appeared in the April 25, 2018, edition of Science Advances.
The interior pressure of large exoplanets (ranging in size between Earth and Neptune) exceeds that at the center of the Earth by more than 10 times—beyond the range of conventional experimental techniques. Thus, the structure and composition of these planetary interiors remains largely unknown. Although scientists know that Earth’s core is composed primarily of iron, research indicates that silicon is likely another major ingredient. “A pure iron core is not realistic, as the process of planetary formation will inevitably lead to the incorporation of significant amounts of lighter elements,” says Raymond Smith, lead researcher from Lawrence Livermore. “Our study is the first to consider these more realistic core compositions.”
The research team used the Omega laser, located at the University of Rochester’s Laboratory for Laser Energetics, to compress iron–silicon alloys to ultrahigh pressures—more than 13 million atmospheres—and then direct a bright x-ray pulse into the test sample to create a diffraction pattern, which provides information on the density and crystal structure of the alloys in the sample. The pressures achieved in the experiments is more than three times the pressure at the center of the Earth and constitutes the highest x-ray diffraction measurements ever reported. Future research will be directed toward understanding how other candidate elements such as carbon or sulfur will affect the structure and density of iron at ultrahigh pressure conditions, as well as measuring other key physical properties of iron alloys needed to constrain plausible models of planetary interior structure and evolution.
Contact: Ray Smith (925) 423-5895 (smith248@llnl.gov).
Livermore scientists have developed a new open-source software application that can compute, analyze, and potentially predict the trajectories of atoms during the course of bond breaking and formation in dynamical simulations. Called TopoMS, the tool could enable breakthroughs in important research areas, such as battery storage and power. The scientists’ research was detailed in the June 2018 issue of the Journal of Computational Chemistry.
In a multiyear initiative involving Lawrence Livermore, Lawrence Berkeley National Laboratory, and the University of Utah, scientists devised a new methodology for performing complex quantum molecular dynamics simulations on supercomputers by combining modern computational science with traditional chemistry and the quantum mechanical theory of atoms in molecules. “We combined highly accurate numerical algorithms with discrete representations that guarantee that the computational analysis is consistent with the theory of smooth functions,” says Livermore computer scientist and lead code developer Harsh Bhatia.
According to Bhatia, TopoMS leverages cutting-edge methods and codes from computational topology to robustly and efficiently compute the Morse-Smale Complex, a mathematical construct used to analyze topology and characterize scalar fields. TopoMS can analyze tens of thousands of atoms at once, eliminating the need for assumptions and producing a much more robust and transferable analysis. In addition, TopoMS is so fast that it could potentially be used in tandem with actual simulations, allowing scientists to observe chemical bonding as it happens. Researchers say the next step is to integrate TopoMS with widely used simulation codes.
Contact: Harsh Bhatia (925) 424-3066 (bhatia4@llnl.gov).