April 19, 2002

High-pressure hydrogen sheds light on Jupiter

Through laser experiments, Lab physicists determined that deuterium, an isotope of hydrogen, turns into a metal at a higher density than research performed at Sandia National Laboratory.

The behavior of hydrogen at extreme pressures provides crucial information on how Jupiter, made primarily of hydrogen, formed and evolved.

LLNL Physicist Robert Cauble will present the Livermore research Sunday at a press conference entitled "Extreme Hydrogen Physics." The presentation will be part of a joint meeting of the American Physical Society and the High Energy Astrophysics Division of the American Astronomical Society in Albuquerque, N.M.

Cauble said the Livermore research shows that laser shocks compressing liquid deuterium at 300 kilobars of pressure — about 300,000 times more than the atmospheric pressure of Earth at sea level — turns the liquid to a metal.

"Hydrogen is all around the universe and a lot of it is at high pressure," Cauble said. "It’s important to know its equation of state, the relationship between pressure, density, and temperature."

Hydrogen’s equation of state dictates at what pressures and densities hydrogen transforms into a metal, and so determines the depth where Jupiter’s metallic hydrogen layer begins and the amount of metallic hydrogen it contains.

In the Livermore experiment, scientists used the now-decommissioned Nova laser to shock-compress liquid deuterium. They found it turned into a metal at a higher density than similar experiments conducted later by Sandia researchers. Using a different technique on Sandia’s Z Machine, Sandia scientists discovered that they also metallized deuterium, but at densities lower than in the laser experiments. The two different equations of state implied by the disparate results affect how researchers view large planets like Jupiter.

Cauble and Marcus Knudson of Sandia will meet to discuss the experimental results, as well as each group’s computer simulations of high-pressure hydrogen during Sunday’s press conference.

Cauble said it’s possible that the groups’ different results both could be right. It may depend on how the sample is shocked.

The research will be applied to inertial confinement fusion where the hydrogen isotopes – deuterium and tritium — are used as fuel to attain fusion. Mega lasers, such as the National Ignition Facility, offer new opportunities for pursuing experimental science under extreme conditions of temperature and density
Cauble said Livermore scientists are conducting further research, using diamond anvil cells to probe the properties of matter under the relevant extreme conditions of pressure and compression found in the interiors of giant gas planets, such as Jupiter.

Other conference presentations featuring Livermore scientists include:

• National Security Fellow Jay Davis of Livermore’s Center for Global Security Research will speak about counter-terrorism contributions from the national labs during the Monday session: "Physics and Anti-Terrorism."

• On Saturday, Physicist Chris Fragile will describe the simulation of black holes "eating" nearby matter, stars and gas clouds and the dynamics of those accretion flows during "The Secret Life of Black Holes."

• Physicist Bruce Remington will describe the new field of high energy density physics in understanding astrophysical phenomena during the Saturday session "Extreme Physics."