Dynamic high pressure: Why it makes metallic fluid hydrogen

Abstract

Metallic fluid H has been made by dynamic compression decades after Wigner and Huntington (WH) predicted its existence in 1935. The density obtained experimentally is within a few percent of the density predicted by WH. Metallic fluid H was achieved by multiple-shock compression of liquid H2, which compression is quasi-isentropic and H is thermally equilibrated in experiments with 100 ns lifetimes. Quasi-isentropic means compressions are isentropic but with sufficient temperature and entropy to drive a crossover from liquid H2 to degenerate fluid H at 9-fold compression and pressure P=140 GPa (1.4 Mbar). The metallic fluid is highly degenerate: T/TF 0.014, where temperature T=3000 K and Fermi temperature TF =220,000 K, respectively, at metallization density 0.64 mol H/cm3. Dynamic compression is achieved by supersonic, adiabatic, nonlinear hydrodynamics, the basic ideas of which were developed in the Nineteenth Century in European universities. Today dynamic compression is generally unfamiliar to the scientific community. The purposes of this paper are to present a brief review of (i) dynamic compression and its affects on materials, (ii) considerations that led to the sample holder designed specifically to make metallic fluid H, and (iii) an inter-comparison of dynamic and static compression with respect to making metallic H.