Crystal structure and temperature of tantalum dynamically compressed to hundreds of gigapascals

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Abstract
We determine the crystal structure and temperature of tantalum ramp and shock ramp compressed to hundreds of gigapascals at the National Ignition Facility. With x-ray diffraction, we find that tantalum remains in the body-centered-cubic structure with no evidence for the proposed phase up to ramp-compression stresses of 531 . 7 − 18.7 + 21.3 GPa . In separate experiments measuring single-shot extended x-ray absorption fine structure (EXAFS) at the L 3 edge, we find that tantalum's temperature agrees well with radiation-hydrodynamics calculations incorporating strength models for ramp and shock-ramp compression to ∼ 200 GPa , but not ∼ 400 GPa . The discrepancy at ∼ 400 GPa can plausibly be explained by underestimated ablation-plasma x-ray heating, with the magnitude of this heating increasing with laser irradiance. These results constitute the highest‐stress structural determination for Ta, the first L -edge EXAFS thermometry in ramp and shock‐ramp experiments, and a stringent benchmark of hydrodynamic models. They validate L ‐edge EXAFS as a robust platform for thermometry in dynamic compression and underscore the need for careful ablator design in future high‐pressure studies.
Funding Information
  • Lawrence Livermore National Laboratory (DE-AC52-07NA27344)

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