Unlocking the Secrets of the Cosmos: Melting Diamond Discovery Paves the Way for Breakthroughs in Fusion Energy and Planetary Science

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Lawrence Livermore National Laboratory has been at the forefront of materials research for decades, and this latest discovery is a testament to the ingenuity and dedication of its scientists.

The study, published in Nature Physics, documents the melting of diamond under pressures three times greater than the conditions at the Earth’s core.

Lead author Marius Millot explained the significance of the discovery: “We were able to take tiny diamond samples and shock compress them to temperatures hotter than the surface of the sun and to pressures higher than the center of Neptune and Uranus—and still measure atomic structure, temperature, density, and optical reflectivity.”

The study resolves two long-standing discrepancies in the field, finally matching experimental results to simulations based on quantum mechanics.

Applying the findings to inertial confinement fusion could triple energy gain, and the new understanding of diamond’s high-pressure phases could reshape models of planetary interiors.

LLNL has been studying diamond’s extreme behavior for decades, with scientists like Jon Eggert and colleagues pioneering high-pressure melting experiments about 20 years ago.

Eggert, a lab scientist, noted: “While this is rather unusual among most materials, we all know an example of such behavior.”

Liquid water is denser than ice, which makes ice cubes float. Jon’s finding means that diamond would float in liquid carbon at high pressures.

The team at LLNL conducted laser-driven dynamic compression experiments at the University of Rochester’s Laboratory for Laser Energetics (LLE) to address both questions.

Using the Omega Laser Facility, the scientists vaporized the outside layer of a tiny sample, sending a squeezing shockwave rocketing through its diamond interior.

Making detailed, unambiguous, and precise measurements during compression was a complicated process.

The high-pressure states were short-lived, lasting for only a billionth of a second.

The team had to capture all the crucial information, including X-ray diffraction data that illuminates atomic structure, in that tiny timeframe.

“This was the first time that shock-compressed diamond was probed with X-ray diffraction all the way up to melting,” said Millot.

The team played a crucial role in developing and maintaining the enhanced diagnostic tools.

Those capabilities led to a new measurement of melting temperature—one that agreed almost perfectly with simulations and closed the 20-year gap.

In contrast to the new, agreed-upon melting temperature, the work told a different story than the phase change that was indicated at Sandia.

The carbon remained in a diamond structure all the way until it melted, skipping any intermediate phases.

Millot explained: “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.”

That difference could be key for future high-energy-density experiments and simulations.

It suggests that material response depends on exactly how the shock is applied, not just on pressure and temperature.

The findings also give planetary scientists a new foothold.

Interiors of ice giants like Neptune and Uranus are essentially inaccessible, so researchers rely on laboratory experiments and models to guess at what’s happening beneath the surface.

Some studies suggest that ice giant planets may crystallize carbon deep in their interior, where it would fall and form ‘diamond rain.’

Because the experiments probed diamond behavior at pressures exceeding those inside ice giants, the latest melting data provides a strong basis for more realistic planetary formation and evolution predictions.

Going forward, the LLNL team plans to leverage the experimental capabilities of NIF to study diamond’s behavior at harder-to-reach, unprecedented extreme conditions.

They aim to refine the understanding of the diamond capsule response in subsequent stages of implosion and to identify the limits of diamond structure stability under a series of multiple shock waves.