Parallax diagnostics of radiation source geometric dilution for iron opacity experiments

Area of Science:

• Plasma Physics
• Astrophysical Opacity Studies
• High-Energy-Density Science

Background:

• Accurate modeling of iron opacity is crucial for understanding stellar interiors.
• Previous opacity models require experimental validation under solar interior conditions.
• Sandia's z-pinch dynamic hohlraum (ZPDH) provides a unique radiation source for such experiments.

Purpose of the Study:

• To experimentally evaluate the accuracy of modeled iron opacity at solar interior conditions.
• To investigate the impact of experimental parameters, specifically source-to-sample distance, on sample heating.
• To refine opacity measurements by accounting for geometric effects.

Main Methods:

• Utilizing the ZPDH radiation source to heat iron samples to 150-200 eV electron temperatures and 7×10^21–4×10^22 cm⁻³ electron densities.
• Employing backlit spectroscopy with four spectrometers at ±9° to measure attenuated radiation.
• Measuring source-to-sample distance using spectrometer parallax to view a half-moon-shaped sample.

Main Results:

• Demonstrated that sample temperature decreases as source-to-sample distance increases.
• Quantified the relationship between source-to-sample distance and iron plasma temperature.
• Highlighted the necessity of considering this geometric effect for accurate opacity inference.

Conclusions:

• The source-to-sample distance is a critical parameter influencing iron plasma temperature.
• Accurate opacity measurements depend on precisely accounting for this geometric factor.
• These findings contribute to validating and improving opacity models for astrophysical applications.