Researchers at Lawrence Livermore National Laboratory have addressed two major unresolved questions in diamond physics through advanced laser-driven compression experiments. The findings, published in Nature Physics, used shock compression techniques at the University of Rochester’s Omega Laser Facility to examine how diamond responds at pressures exceeding those found at Neptune and Uranus’s centers.
The study resolved a persistent discrepancy in diamond melting temperatures that had puzzled scientists for approximately two decades. Previous laboratory measurements had differed by roughly 20 percent from theoretical predictions based on quantum mechanical simulations. Using improved X-ray diffraction diagnostics, researchers obtained new measurements that aligned almost perfectly with computer models, effectively ending the long-standing disagreement. The team also confirmed an earlier finding that liquid diamond is denser than solid diamond—a counterintuitive property similar to how ice floats in water.
The experiments also addressed questions raised by prior research conducted at Sandia National Laboratories, which had suggested diamond might pass through an intermediate crystalline structure before fully melting. However, the new measurements showed that diamond maintains its crystalline structure all the way to the point of melting into liquid carbon, with no intermediate phase occurring. Researchers attributed this to the brief duration of shock compression, which does not allow sufficient time for structural transformation.
These findings have practical implications for inertial confinement fusion research, where diamond capsules are compressed by lasers to generate fusion reactions. The revised understanding of diamond’s melting behavior suggests that initial shocks could be moderately reduced in intensity while still achieving complete capsule melting. This adjustment could potentially improve fuel compressibility and energy gain in fusion experiments. Additionally, the clarified model of diamond behavior under extreme conditions may enhance scientists’ understanding of planetary interiors within ice giant planets like Neptune and Uranus.
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