X-ray Thomson scattering studies on spin-singlet stabilization of highly compressed H-like Be ions heated to two million degrees Kelvin

TL;DR

This study analyzes high-temperature, highly compressed hydrogen-like beryllium plasmas created at NIF, revealing spin-singlet pairing and providing a simplified, rapid data analysis method that aligns well with experimental observations.

Contribution

The paper introduces a simplified first-principles average-atom approach for analyzing NIF plasma data, demonstrating its effectiveness and physical transparency compared to complex simulation methods.

Findings

NIF data suggests a density of 20±2 g/cm³ and temperature around 1.8 million K.

Evidence of high-T spin-singlet pairing of hydrogen-like Be ions.

Structure factor calculations support revised plasma parameters.

Abstract

Experiments at the US National Ignition Facility (NIF) [D\"{o}ppner et al., Nature {\bf 618}, 270-275 (2023)] have created highly compressed hot hydrogen-like Be plasmas. Published analyses of the the NIF experiment have used finite-$T$ multi-atom density-functional theory (DFT) with Molecular dynamics (MD), and Path-Integral Monte Carlo (PIMC) simulations. These methods are very expensive to implement and often lack physical transparency. Here we (i) relate their results to simpler first-principles average-atom results, (ii) establish the feasibility of rapid data analysis, with good accuracy and gain in physical transparency, and (iii) show that the NIF experiment reveals high-$T$ spin-singlet pairing of hydrogen-like Be ions with near neighbours. Our analysis predicts such stabilization over a wide range of compressed densities for temperatures close to two million Kelvin. Calculations of structure factors $S(k)$ for electrons or ions, the Raleigh weight and other quantities of interest to X-ray Thomson scattering are presented. We find that the NIF data at the scattering wavevector $k_{sc}$ of 7.89 \AA$^{-1}$ are more consistent with a density of $20\pm2$ g/cm$^3$, mean ionization $\bar{Z}=$3.25, at a temperature of $\simeq$ 1,800,000 K than the 34 g/cm$^3, \bar{Z}=3.4$ proposed by the NIF team. The relevance of ion-electron coupled-modes in studying small $k_{sc}$ data is indicated.