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Magnesium Oxide’s Dynamic Transition
Magnesium oxide (MgO) is a crucial component of Earth’s lower mantle and is believed to play a similar role in the mantles of massive rocky exoplanets. Due to this geophysical significance, scientists have sought to understand MgO’s behavior under extreme conditions. Researchers from Lawrence Livermore with collaborators from Johns Hopkins University, the University of Rochester, Princeton University, and SLAC National Accelerator Laboratory devised an experimental platform to pinpoint the pressure at which a critical transition in MgO’s structure—from a simple rock salt (B1) crystal structure to a cesium chloride (B2) structure—is expected to occur within super-Earths. This transformation alters MgO’s properties, such as viscosity, to affect a planet’s internal dynamics.
The platform combined laser-shock compression with simultaneous measurements of pressure, crystal structure, temperature, microstructural texture, and density. Using the Omega EP and Omega 60 lasers at the University of Rochester’s Laboratory for Laser Energetics Omega Laser Facility, the team compressed MgO to pressures up to 634 gigapascals (GPa) for several nanoseconds, then probed MgO’s atomic structure with a nanosecond x-ray source. The researchers found that the B1 to B2 phase transition occurred at approximately 9,700 Kelvin within 400–430 GPa. B2-liquid coexistence was observed beyond 470 GPa, and complete melting occurred at 634 GPa. Their results are published in the June 7, 2024, issue of Science Advances. Livermore scientist Ray Smith, one of the authors, says, “This study provides the first direct atomic-level and thermodynamic constraints of the pressure–temperature onset of the B1 to B2 phase transformation and represents the highest temperature x-ray diffraction data ever recorded.”
Contact: Ray Smith (925) 423-5895 (smith248 [at] llnl.gov (smith248[at]llnl[dot]gov)).
Solvers Optimized for Supercomputers
In high-performance computing, preconditioner solvers are often used in complex mathematical algorithms to improve the speed and accuracy of simulation results. A team of researchers including Livermore computational mathematician Tzanio Kolev and former Livermore staff now at Portland State University introduced specialized solvers optimized for running simulations on graphics processing units (GPUs), such as those in Livermore’s exascale supercomputer El Capitan. (See “Introducing El Capitan.”) The team’s algorithms solve the radiation diffusion equations underpinning MARBL, a mission-critical hydrodynamics code. Results of this work were published June 30, 2024, in the SIAM Journal on Scientific Computing.
The new solvers increase the speed of computation by subdividing physical systems into H(div), a finite element space. H(div) is one of four finite element spaces in a set of differential equations known as the de Rham complex, all of which are incorporated into the Livermore-led MFEM (Modular Finite Element Methods) software library. H(div) was the last space for which development of efficient solvers was required. To meet this need, the team abandoned matrix-based algorithms that can become too large to compute efficiently and reformulated the problem in the context of a saddle-point system, which resembles a riding saddle when plotted on a graph. With this approach, the team expanded the original, tightly packed formulation into a more solvable one. Says Kolev, “After considering this problem for a long time, we now have state-of-the-art methods in all of the de Rham spaces.”
Contact: Tzanio Kolev (925) 423-9797 (kolev1 [at] llnl.gov (kolev1[at]llnl[dot]gov)).
3D Printing Complex Biological Structures
Livermore engineers have reviewed the landscape of multiscale and multimaterial 3D printing and explored hardware and processes best poised to emulate the self-organizing abilities of biological materials. Their paper, published in the August 22, 2024, issue of Advanced Materials, highlights the potential for creating complex structures found in biological systems with high resolution and speed. Further, the paper explains that multimaterial 3D printing is a crucial factor in modulating and programming material properties of such structures.
The paper also covers recent additive manufacturing developments in fabricating structures with diverse materials across different scales, the evolution of manufacturing processes, and the necessity of scalable solutions for biological materials printing to address gaps between size ranges. Despite emerging technologies enabling innovations such as parallel printing of complex 3D structures, no single technology has been able to provide both high resolution and high throughput over a range of materials. The Livermore team proposes to address remaining needs with co-design of materials and processes, integration of automated systems, and the extension of existing methods to a broader range of functional materials. “Multiscale and multimaterial 3D printing is redefining what’s possible in future manufacturing, enabling us to design and fabricate complex, integrated systems that seamlessly combine materials with diverse properties,” says Cheng Zhu, one of the paper’s authors. “The breakthrough in this area not only expands the horizons of material science but also paves the way for transformative applications in multiple industries ranging from healthcare to aerospace.”
Contact: Cheng Zhu (925) 423-5503 (zhu6 [at] llnl.gov (zhu6[at]llnl[dot]gov)).
