William J. Nellis

In 2003, Nellis retired from LNLL and joined the Department of Physics at Harvard University as an Associate. Since leaving LLNL, Nellis has collaborated with scientists in Japan, Russia, China and Sweden, as well as in the United States.

Nellis has also been involved with the International Association for the Advancement of High Pressure Science and Technology, AIRAPT, for the greater part of his career serving as the vice president from 1999 to 2003 and as the president from 2003 to 2007. From 1998 to 2007, he served as the editor of the journal Shock Waves.

In 1976, Nellis moved within LLNL to the High-Dynamic-Pressure Experimental Group, in which he measured properties of approximately 30 cryogenic liquids and solids compressed dynamically to pressures in the range 20-500 GPa with associated temperatures up to as much as several 1000 Kelvins. Those molecular fluids are representative of fluids in the interiors of Giant Planets and in reacted high explosives. Those temperatures, pressures and densities were generated by impact of a high-velocity projectile onto a target material. Impactors were accelerated with a two-stage light-gas gun to velocities as large as 8 km/s (18,000 mph). Impactors were typically 25 mm in diameter and 2–3 mm thick. Samples were 25 mm in diameter and 0.5 – 3 mm thick. Experimental lifetimes were around 100 nanoseconds. Fast electrical and optical measurements were made with detectors having sub-ns resolution time.

From 1970 to 1973, Nellis was Assistant Professor of Physics at Monmouth College (ILL) where he taught undergraduate physics courses and was Director of the College’s Computer Center. In 1973, he left Monmouth to join Lawrence Livermore National Laboratory (LNLL), where he performed computational simulations of condensed matter under dynamic compression driven by shock waves generated with high explosives.

William J. Nellis (born June 25, 1941) is an American physicist. He is an Associate of the Physics Department of Harvard University. His work has focused on ultra-condensed matter at extreme pressures, densities and temperatures achieved by fast dynamic compression. He is most well-known for the first experimental observation of a metallic phase of dense hydrogen, a material predicted to exist by Eugene Wigner and Hillard Bell Huntington in 1935.

Nellis was born in Chicago, Illinois in 1941. He received his B.S. degree in Physics from Loyola University of Chicago, College of Liberal Arts and Sciences, in 1963 and his Ph.D. degree in Physics from Iowa State University in 1968. His Ph.D. thesis research included measurements of electrical and thermal conductivities of single crystals of the Rare Earth elements Gadolinium, Terbium and Holmium in the Ames National Laboratory at Iowa State.

Nellis is most well-known for the first experimental observation of a metallic phase of dense hydrogen, a material predicted to exist by Wigner and Huntington in 1935. Dynamic compression generates temperature T and entropy S on rapid compression and the product TS controls phase stability via the free energy. By tuning the magnitude and temporal shape of a reverberating shock pressure pulse, H2 dissociates to H at sufficiently large density that measured electrical conductivities of fluid H cross over from semiconducting to degenerate metal with Mott’s Minimum Metallic Conductivity at pressure 1.4 million bars (140 GPa), nine-fold H atom density in liquid H2 and calculated temperature of 3000 K. Similar electrical conductivities of H under multiple-shock compression have been measured by Fortov et al. Celliers et al at the NIF pulsed laser have measured optical reflectivity of dense fluid metallic D of ~0.3 under multiple-shock compression, which value agrees with the inception of metallization of D calculated by Rillo et al. Measured electrical conductivities of fluid SiH4 up to 106 GPa under multiple-shock compression with a two-stage light-gas gun are in good agreement with the electrical conductivity data measured in.