Oxygen Opacity Measurements at High-Energy-Density Conditions

Area of Science:

• Plasma Physics
• Astrophysics
• Atomic Physics

Background:

• Understanding stellar interiors requires accurate opacity data at high energy densities.
• Previous opacity measurements have limitations in this regime.

Purpose of the Study:

• To present the first benchmark measurements of oxygen opacity at high-energy-density.
• To compare experimental results with existing theoretical opacity models.

Main Methods:

• A 3-5 μm thick SiO2 sample was heated using a Z facility x-ray source.
• Opacity was measured in the 5-19.5 Å range using multiple spectrometers.
• Electron temperature and density were inferred from Si K-shell spectra.

Main Results:

• Electron temperature was 148±4 eV and density was 8.6±1.4×10^21 cm^-3.
• Six experiments demonstrated opacity reproducibility within ±15%.
• Measured oxygen opacity showed excellent agreement with seven different theoretical models.

Conclusions:

• The measurements provide crucial data for astrophysical simulations.
• Discrepancies near the H-like photon ionization threshold and spectral lines indicate a need for theoretical model refinement.
• This work validates and guides improvements in opacity calculations for stellar interiors.