The 8th International Conference on Matter and Radiation at Extremes (ICMRE2025)

75 / 2025-03-11 17:49:36

Laboratory Measurement of L-Shell Opacity at GEKKO XII/LFEX High Power Laser Facility

High energy density laboratory astrophysics,plasma opacity,Spectrum Analysis,hohlraum

Opacity governs radiation energy transport in high-energy-density (HED) plasmas and is essential for understanding stellar interiors and inertial confinement fusion. However, the complexity of atomic calculations often leads to discrepancies in opacity models. One possible reason for the disagreement between solar models and helioseismology observations is the underestimation of theoretical opacities.[1] Experimental validation is therefore crucial for astrophysics and HED science.

The first plasma opacity measurement above 150 eV and electron densities exceeding 10²²/cm³ was conducted at Sandia’s Z facility, revealing significant discrepancies between experimental data and model predictions in conditions relevant to the solar convection-radiative boundary.[2] The study proposes a hypothesis that some key atomic processes may be missing in current opacity models.[3]

In this work, we present opacity measurements at the GEKKO XII laser facility, using a laser-driven hohlraum to heat calcium and titanium samples to an open L-shell state while avoiding direct laser heating. High-temporal-resolution diagnostics were achieved with the LFEX picosecond laser. Our experiments confirm that optimized hohlraum geometries and laser energies yield radiation temperatures of 80–90 eV with a 1.3 ns pulse. For the first time at GEKKO/LFEX, temporally resolved transmission, sample emission, and backlight emission spectra were obtained, providing essential benchmarks for opacity calculations. These results could contribute to improving opacity modeling and advancing radiation transport modeling in HED plasmas.

[1] S. Basu, H. M. Antia, Physics Reports 457, 217-283 (2008).

[2] J. E. Bailey et al., Nature 517, 56-59 (2015).

[3] T. Nagayama et al., Phys. Rev. Lett. 122, 235001 (2019).