Sandia Labs FY22 Laboratory Directed Research & Development Annual Report

SIMULATED X-RAY DIFFRACTION AND MACHINE LEARNING FOR OPTIMIZING DYNAMIC EXPERIMENT ANALYSIS.

In-situ X-ray diffraction (XRD) from ns dynamic compression experiments is shedding light on atomistic processes at extreme pressures. As experiments develop, new computational analysis tools are necessary to make sense of the data. This one-year LDRD project successfully established a simulated XRD capability and proved the concept

of applying ML image analysis to interpret experimental data. The team developed code and validated new LAMMPS tools for 2D XRD pattern creation, produced cadmium sulfide (CdS) 2D XRD training data for two structures, incorporating broad X-ray spectrum. ML pattern recognition models (convolutional neural network-based) were trained from this dataset for orientation analysis and noise filtering. The ability to simulate and analyze X-ray diffraction data is crucial to interpreting a new class of dynamic high-pressure experiments. The success of this one-year project, presented at multiple American Physical Society conferences, advances predictive capability within weapons science. (PI: J. Matthew D. Lane)

Representation of a reciprocal lattice density (black) and Ewald sphere construction (white) in k-space. The points intersecting the Ewald sphere of radius 1/λ represents the monochromatic diffraction pattern for that energy X-ray. The orientation of the sphere is determined by the incident k vector. The 2D diffraction pattern is mapped on the spherical surface with angular coordinates θ and φ.

Top: Real-space atomistic representations of CdS phase transition under high-pressure (> 5.5 GPa) shock compression colored by lattice type and orientation. Wurtzite is black. Rock salt is green, red or blue, based on orientation. Middle: Simulated diffraction patterns from the atomistic simulations, produced with energy spectrum and angular geometry corresponding to experiments. Because DCS X-rays are highly collimated, a single incident angle was used. Bottom: Experimental patterns showing evolution from wurtzite to rock salt structures. Time progresses from left to right. Experiments correspond with experimental times -43, 110, and 263 ns.

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LABORATORY DIRECTED RESEARCH & DEVELOPMENT