High Precision Hugoniot Measurement of Aluminum up to 90 Mbar on the 100 kJ Laser Facility

Aluminum is the standard material for ultrahigh pressure impedance matching experiments, yet its principal Hugoniot above 50 Mbar, where inner shell ionization dominates, lacks precise experimental data. Here we report laser driven Hugoniot measurements of aluminum at 89 and 93 Mbar using an indirect drive hohlraum on a 100 kJ laser facility. The shock velocities were determined with a combined uncertainty below 0.5% using a dual diagnostic approach. With quartz as the impedance matching standard, the measured compression ratios are 4.47±0.17 and 4.58±0.18. These results agree with models that include shell effects, including extended first principles molecular dynamics, stochastic density functional theory, and the Hartree–Fock–Slater model with charged hard spheres, but deviate by 8–10% from average atom models such as SESAME. These results validate shell‑resolved equation‑of‑state models against average‑atom predictions in the hundred‑megabar regime, and provide a quantitative benchmark confirming that L‑shell ionization softens the aluminum Hugoniot. This establishes a long‑sought high‑precision reference that supports aluminum as a standard for ultrahigh‑pressure impedance matching.