Shell mix in the compressed core of spherical implosions

Area of Science:

• Plasma Physics
• Nuclear Fusion
• Astrophysical Phenomena

Background:

• The Rayleigh-Taylor instability, particularly in its nonlinear, turbulent phase, is a critical phenomenon in inertial confinement fusion (ICF).
• This instability drives atomic-scale mixing between the ablator shell material and the deuterium-tritium fuel within the compressed core of ICF targets.
• Understanding this mixing is crucial for accurately assessing core conditions and fusion yields.

Purpose of the Study:

• To quantify the density of shell material mixed into the fuel core during direct-drive plastic-shell spherical-target implosions.
• To determine the fuel density within the compressed core.
• To compare the estimated fuel density with the neutron-burn-averaged electron density.

Main Methods:

• Utilized time-resolved X-ray spectroscopy to probe the mixed shell material.
• Employed charged-particle spectroscopy for complementary measurements of core conditions.
• Analyzed core X-ray images to reconstruct target structure and density profiles.

Main Results:

• Estimated the density of shell material mixed into the outer core at 3.4(+/-1.2) g/cm³.
• Determined the fuel density in the compressed core to be 3.6(+/-1) g/cm³.
• Found that the estimated fuel density accounts for only approximately 50% of the neutron-burn-averaged electron density (n(e)=2.2(+/-0.4)x10²⁴ cm⁻³).

Conclusions:

• The significant mixing of shell material into the fuel core, as evidenced by density measurements, impacts the accuracy of fusion performance predictions.
• The discrepancy between fuel density and electron density highlights the complex physics governing ICF core conditions.
• Further research is needed to refine models of turbulent mixing and its effect on fusion energy gain.