Scientists achieve over 1.5 million atmospheres on diamond, solving bonding mystery

Scientists have smashed diamond to pressures over 1.5 million atmospheres—exceeding the crushing forces inside Neptune and Uranus—using a laser‑driven shock experiment at the National Ignition Facility. The data, released Tuesday, confirm the long‑sought transition from diamond’s normal sp³ bonding to a denser sp² phase, settling a 20‑year theoretical dispute that had puzzled physicists and astronomers alike. The study was led by Dr. Maria Sokolova of the University of California, Berkeley, and published in *Science*.

The experiment matters because diamond’s high‑pressure behavior governs two frontier fields. In fusion research, diamond anodes and targets are used to confine plasma; knowing how diamond compresses and melts under extreme conditions can boost energy output and reduce energy losses. In planetary science, the dense, “diamond rain” thought to fall through the interiors of ice giants depends on how carbon atoms rearrange when squeezed by millions of atmospheres. Earlier models predicted a gradual change, while spectroscopic observations of Neptune’s atmosphere suggested a sudden shift, leaving the community uncertain.

Using a 600‑kilojoule laser pulse, the team created a shock front that accelerated a thin diamond slab to 1.5 megabars in less than 10 picoseconds. X‑ray diffraction and Raman spectroscopy captured the crystal’s structural evolution in real time. The results show a sharp, reversible transition at 1.2 megabars, matching quantum‑mechanical calculations that had been dismissed as unrealistic. The team also measured the new phase’s electrical conductivity, finding it rises by an order of magnitude—an insight that could help designers of next‑generation fusion reactors.

With the mystery solved, researchers can now refine fusion target designs to exploit diamond’s high‑pressure phase, potentially improving confinement and reducing the energy required to reach ignition. Planetary scientists will use the data to model the composition and dynamics of ice‑giant interiors, informing future missions to Uranus and Neptune. The work also opens the door to studying other light elements under extreme conditions, bringing us closer to understanding the physics that powers both stars and exotic planets.