Equilibration dynamics and conductivity of warm dense hydrogen

Area of Science:

• Plasma Physics
• Materials Science
• Ultrafast Dynamics

Background:

• Understanding the behavior of warm dense matter is crucial for various fields, including inertial confinement fusion and astrophysics.
• Experimental data on the dynamic properties of hydrogen under these extreme conditions are scarce.

Purpose of the Study:

• To investigate the subpicosecond dynamics of warm dense hydrogen.
• To determine the energy transfer rate between electrons and ions.
• To validate plasma models and transport property calculations.

Main Methods:

• Utilizing the XUV free-electron laser facility (FLASH) for ultrafast impulsive electron heating with X-rays.
• Employing time-delayed X-ray scattering to probe the sample dynamics.
• Performing radiation hydrodynamics simulations with Saha and Thomas-Fermi ionization models.
• Validating a conductivity model using two-temperature density-functional theory and molecular dynamics simulations.

Main Results:

• Observed dissociation of molecular hydrogen within (0.9 ± 0.2) picoseconds.
• Inferred electron-ion energy transfer rates.
• Predicted plasma parameters and calculated the static structure factor.
• Validated a conductivity model for partially ionized plasma against experimental data.

Conclusions:

• The study provides critical experimental insights into the ultrafast dynamics of warm dense hydrogen.
• The validated conductivity model offers a reliable method for predicting transport properties of dense plasmas.
• This research contributes essential data for theoretical models and future experiments in plasma physics.