Highly compressed spin-singlet Be at a million Kelvin

Area of Science:

• Plasma Physics
• Quantum Chemistry
• Materials Science

Background:

• Experiments at the U.S. National Ignition Facility (NIF) have produced highly compressed hot hydrogenlike Beryllium (Be) plasmas.
• Previous analyses relied on computationally expensive methods like finite-temperature multiatom density-functional theory and Path-Integral Monte Carlo simulations, often lacking physical transparency.

Purpose of the Study:

• To relate complex simulation results to simpler first-principles average-atom calculations.
• To establish a feasible method for rapid data analysis with improved accuracy and physical transparency.
• To investigate high-temperature spin-singlet pairing of hydrogenlike Be ions within the NIF experiment.

Main Methods:

• Utilized first-principles average-atom calculations for comparison with existing NIF data.
• Performed rapid data analysis to assess accuracy and physical transparency.
• Calculated structure factors S(k), Raleigh weight, and other X-ray Thomson scattering diagnostics.

Main Results:

• The NIF experimental data at k_sc = 7.89 Å⁻¹ are more consistent with a Be plasma density of 20±2 g/cm³ and mean ionization Z̄=3.25 at T ≃ 1,800,000 K.
• This contrasts with the NIF team's proposed parameters of 34 g/cm³ and Z̄=3.4.
• High-temperature spin-singlet pairing of hydrogenlike Be ions with near neighbors was identified, predicting stabilization over a wide density range near 2 million Kelvin.

Conclusions:

• The study demonstrates the feasibility of rapid, transparent, and accurate analysis of NIF plasma data using simpler theoretical approaches.
• The findings suggest a revised understanding of the plasma conditions in the NIF experiment, particularly regarding density and ionization.
• The observed spin-singlet pairing offers insights into plasma stabilization mechanisms at extreme conditions relevant to inertial confinement fusion.