Researchers at Lawrence Livermore National Laboratory used the Omega Laser Facility to shock-compress diamond samples to extreme temperatures and pressures. The laser experiments closed a 20-year scientific disagreement, proving that carbon retains its diamond structure until melting and potentially paving the way for triple energy gains in nuclear fusion.
Scientists have finally settled a two-decade debate over how diamond behaves at its breaking point. Researchers at Lawrence Livermore National Laboratory tracked synthetic diamond samples as they were shock-compressed to pressures reaching one terapascal—roughly three times greater than the conditions at Earth’s core. The findings resolve a persistent 20-year gap between experimental data and quantum-based theoretical simulations.
Laser-Driven Shocks at the Omega Laser Facility
To capture diamond at the edge of its transformation, researchers turned to the University of Rochester’s Laboratory for Laser Energetics. At the Omega Laser Facility, teams fired powerful ultraviolet laser pulses at tiny synthetic diamond samples to drive intense shock waves through the material.
The compressed states lasted for only a billionth of a second. During that brief window, scientists measured shock speed, reflectivity, thermal radiation, and X-ray diffraction to observe atomic structures. Carbon atoms are lightweight and scatter very few X-rays, making the necessary signal faint and difficult to isolate.
“This was the first time that shock-compressed diamond was probed with X-ray diffraction all the way up to melting. These measurements are extremely difficult because carbon is a small and lightweight atom. It scatters very few X-rays, so the signal we needed to measure was quite faint.”
Marius Millot, LLNL scientist
The campaign included 12 steady-shock experiments and seven experiments utilizing shocks that weakened as they traversed the sample. The resulting data revealed a broad melting region between approximately 750 and 1,000 gigapascals, where shock temperature decreased slightly as pressure rose.
Closing a 20-Year Discrepancy in Temperature and Density
Decades ago, laboratory experiments led by Jon Eggert established that diamond becomes denser when it melts under high pressure—an unusual behavior mirrored by water, where liquid water is denser than ice, which makes ice cubes float. That landmark discovery introduced a stubborn problem that lingered for roughly 20 years: measured melting temperatures differed from theoretical quantum-mechanical predictions by about 20 percent.
“No matter what the theorists did – even with the most advanced computer simulation techniques – they could not reproduce the experiments.”
Marius Millot, LLNL scientist
The newly upgraded diagnostics helped close a gap where original temperature measurements had been off by more than 1,000 degrees. While the realization was frustrating for researchers, the dramatic leap in data quality allowed scientists to confirm their original inference of melting directly through X-ray diffraction.
Skipping Intermediate Phases Under Single-Shock Compression
The experiments also addressed a competing hypothesis stemming from research at LLNL. Work using the Z machine’s extreme magnetic fields had been interpreted as an indication that diamond transforms into an intermediate crystalline structure known as BC8 before ultimately liquefying.
The Lawrence Livermore team found no such transition. X-ray diffraction data showed that the compressed solid retained its ordinary cubic diamond structure right up until the moment of melting. Researchers noted that assigning the measured diffraction peak to the proposed BC8 structure would produce density values roughly 30 percent away from earlier measurements, while lacking the required secondary diffraction lines.
“We think that is because the sample does not have time to change when it only experiences a single shock. It remains ‘trapped’ in the diamond structure.”
Marius Millot, LLNL scientist
Implications for Inertial Confinement Fusion and Planetary Interiors
Beyond resolving atomic-scale debates, the findings carry practical implications for clean energy research. Diamond forms the solid pellet that encases nuclear fuel for inertial confinement fusion. Understanding how the material melts under extreme conditions could allow for weaker initial shocks in future experiments, potentially increasing energy output by a factor of three.
The revised high-pressure phase models also reshape theoretical frameworks for understanding planetary interiors. Scientists believe that carbon in the form of diamond rains down deep inside ice giant planets like Neptune and Uranus. With precise benchmarks now established for quantum simulations, researchers possess a clearer picture of both laboratory fusion targets and the extreme mechanics governing distant worlds.
Worth a look
Antarctica’s Blood Falls Hosts Marine Microbes Sealed for Millions of Years
Sealed beneath Antarctica's Taylor Glacier for more than a million years, Blood Falls discharges a rust-red brine fed...
Exoplanet Spin Measurements Risk Capturing Atmospheric Winds
Astronomers warn that measuring the rotation of distant exoplanets often captures atmospheric winds rather than a planet's true...
NASA Engineers Extend Voyager 2 Mission Life Into 2028 With Power Strategy
NASA engineers running the Voyager 2 spacecraft have successfully executed a power-switching strategy dubbed the "Big Bang," extending...
Milwaukee Landlord Finds Stolen Pablo Picasso Print in Vacant Apartment
A rare Pablo Picasso etching stolen from a Milwaukee art gallery in 2018 has been recovered after a...