Researchers at Lawrence Livermore National Laboratory have conducted experiments that resolve long-standing questions about how diamond behaves under extreme pressure conditions. Using laser-driven dynamic compression techniques at the University of Rochester’s Laboratory for Laser Energetics, the team subjected tiny diamond samples to pressures exceeding those found at the centers of Neptune and Uranus while measuring their atomic structure and properties. The findings were published in Nature Physics.
The research addressed two major puzzles in diamond physics that had persisted for approximately two decades. Earlier experiments had measured diamond melting temperatures that differed by roughly 20 percent from theoretical predictions, creating a significant discrepancy that researchers could not resolve. Additionally, separate experiments suggested diamond might transform into an intermediate crystalline phase before fully melting, but this intermediate state had never been directly confirmed. The new measurements provided direct X-ray diffraction observations of shock-compressed diamond, enabling researchers to track the material’s atomic arrangement through the melting process.
The experiments revealed that diamond maintains its crystalline structure until it melts completely into liquid carbon, with no intermediate phase appearing during the shock compression. The updated melting temperature measurements now align closely with quantum mechanics-based computer simulations, resolving the long-standing disagreement between experimental and theoretical results. Researchers attribute the earlier temperature discrepancies partly to improved diagnostic equipment and measurement techniques developed specifically for detecting faint X-ray signals from carbon atoms.
These findings have practical implications for inertial confinement fusion research, where diamond capsules are used to contain fusion fuel. The new understanding of diamond’s melting behavior suggests that researchers may be able to use slightly weaker initial shock waves while still achieving complete capsule melting, potentially making fusion fuel more compressible and improving energy gain by a factor of three. The results also provide clearer insights into planetary interiors, particularly for ice giants where scientists believe diamonds may form and precipitate beneath the surface.
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