Alumnus Puts Hydrogen Under Pressure in Experiments

A Department of Energy National Nuclear Security Administration Stewardship Science Graduate Fellowship (DOE NNSA SSGF) alumnus is lead author on a Nature Communications paper providing insight into hydrogen’s behavior under extreme pressures. The results have implications for planetary science and fusion energy research.

The experiments used Lawrence Livermore National Laboratory’s Jupiter Laser Facility to measure the pressures at which deuterium, a hydrogen isotope, begins to change from an insulator to a metal. Alumnus Paul Davis conducted the research at Livermore Lab while a graduate student at the University of California, Berkeley. He is now a science and technology policy fellow at the Department of Defense.

The researchers used one beam on the Janus laser to shock a deuterium capsule, a Livermore Lab release says. A second beam created X-rays that scattered off the shocked hydrogen. The scattered rays were spread into a spectrum similar to how a prism breaks sunlight into a rainbow.

The scientists examined spectra generated over a range of shock pressures and compared them to theoretical calculations to determine when free electrons begin to appear, indicating that the hydrogen is turning from an insulator to a metal.

The research helps understand the physics inside giant planets like Jupiter, Davis said in the release, especially how electrically conductive hydrogen contributes to the dynamo action that creates their magnetic fields. The same pressures come into play in experiments at Livermore’s National Ignition Facility, where scientists use massive lasers to squeeze hydrogen so tightly the atoms fuse, releasing tremendous energy.

Davis earned his doctorate in 2012, the same year he finished the fellowship.