Investigating the insulator to metal transition in dense fluid hydrogen with dynamic compression on NIF*

Despite extensive theoretical and experimental advances in the past decades, the properties of fluid hydrogen remain challenging to understand in the vicinity of the predicted first-order insulator-to-metal transition, also known as the plasma phase transition. Recent static and dynamic compression studies provide evidence for the insulator-metal transition in fluid hydrogen and deuterium at temperatures less than 2000 K but disagree on both the nature and pressure of the transition. There are also discrepancies in theoretical calculations with transition pressures spanning 120 GPa to 400 GPa at these temperatures. We present recent experiments using a reverberation compression scheme on the National Ignition Facility to compress cryogenic deuterium up to 600 GPa at much lower temperatures than along the principal Hugoniot. Our optical measurements reveal a high index of refraction along with the onset of visible absorption, both arising from band gap closure ranging from 120 to 150 GPa (depending on temperature). Metallic reflectivity appears above 1000 K and 200 GPa. These results complement recent static and dynamic compression studies.