Researchers at Lawrence Livermore Nationwide Laboratory have documented how diamond melts beneath excessive stress, resolving a decades-long scientific thriller and probably opening the trail to triple the vitality acquire in fusion experiments. In a examine revealed in Nature Physics on August 13, 2026, scientists led by Marius Millot used shock-compression strategies to soften diamond samples at pressures 3 times better than the circumstances at Earth’s core.
The experiments lastly reconciled a cussed battle: for practically 20 years, the measured melting temperature of diamond differed by roughly 20 % from what quantum-mechanical simulations predicted. “It doesn’t matter what the theorists did—even with essentially the most superior laptop simulation strategies—they might not reproduce the experiments,” Millot stated.
Resolving the Thriller
To handle the discrepancy, the LLNL staff performed laser-driven dynamic compression experiments on the College of Rochester’s Laboratory for Laser Energetics utilizing the Omega Laser Facility. The scientists vaporized the skin layer of tiny diamond samples, sending shock waves rocketing by means of the inside at pressures between 600 gigapascals and 1.8 terapascals—circumstances hotter than the solar’s floor and exceeding the stress on the facilities of Neptune and Uranus.
The important thing innovation was measuring X-ray diffraction information throughout melting, a feat that had by no means been completed earlier than. “These measurements are extraordinarily troublesome as a result of carbon is a small and light-weight atom. It scatters only a few X-rays, so the sign we wanted to measure was fairly faint,” Millot defined. The brand new measurements put diamond’s melting temperature at round 7,300 Kelvin at 1 terapascal, considerably decrease than the outdated experimental readings and in settlement with theoretical predictions.
The experiments revealed one other shocking discovering: diamond doesn’t remodel into an intermediate crystalline part known as BC8 earlier than melting, as some earlier theories instructed. As a substitute, the carbon stays locked in its acquainted diamond crystal construction all the way in which till it melts into liquid carbon. “We predict that’s as a result of the pattern doesn’t have time to vary when it solely experiences a single shock. It stays ‘trapped’ within the diamond construction,” Millot stated.
One of the counterintuitive outcomes is that stable diamond is definitely much less dense than the liquid carbon it melts into—a property it shares with ice and water. This implies diamond might theoretically float in molten carbon at these excessive pressures, an uncommon conduct amongst most supplies.
Implications for Fusion Vitality
The findings have direct penalties for inertial confinement fusion, the strategy used on the Nationwide Ignition Facility. In these experiments, highly effective lasers generate shock waves that drive a tiny diamond capsule inward, compressing fusion gas to the acute pressures and temperatures wanted for nuclear reactions. Melting the diamond capsule right into a uniform fluid throughout the preliminary shock is essential to attenuate implosion imperfections that may scale back fusion yield.
Present NIF protocols use comparatively sturdy first shocks to make sure the diamond melts fully. However the brand new analysis suggests scientists might use barely slower preliminary shocks and nonetheless obtain full melting. “That is thrilling as a result of such a slower shock would make the fusion gas extra compressible. That in flip will increase the utmost vitality yield we might receive with the identical laser vitality,” Millot stated. Pc simulations incorporating the up to date carbon mannequin predict that these slower shocks might triple vitality acquire, supplied different degradation mechanisms will be managed.
The work additionally extends past fusion. The findings present planetary scientists with a stronger foundation for understanding the interiors of ice big planets like Neptune and Uranus, the place carbon might expertise comparable excessive pressures and will kind “diamond rain” deep beneath the floor. The brand new melting information will assist refine fashions of planetary formation and evolution in these distant worlds.
Sources
- Lawrence Livermore Nationwide Laboratory — official announcement and quotes from Marius Millot and Jon Eggert on diamond melting experiments, stress circumstances, and fusion implications
- Nature Physics — peer-reviewed publication of the examine “Diamond melting in shock compression experiments at 1 TPa pressures” (August 2026)
- ScienceAlert — detailed rationalization of experimental strategies, X-ray diffraction measurements, and the absence of BC8 part transition
- Phys.org — reporting on the decision of the 20-year temperature discrepancy and fusion vitality acquire predictions
