Scientists at Lawrence Livermore National Laboratory have recreated the extreme conditions thought to produce "diamond rain" deep inside ice giants such as Neptune and Uranus. Using a powerful laser, researchers briefly subjected diamond to pressures more than three times those at Earth's core and temperatures comparable to the sun's surface. X-ray measurements allowed them to pin down diamond's melting behavior, resolving a decades-old disagreement between experiments and computer models. They also found that solid diamond can be less dense than extremely hot liquid carbon, meaning diamonds could float under certain conditions. The results provide new experimental support for models of diamond formation and movement inside giant planets, where such processes may help explain Neptune's unusual internal heat.
The experiment could also have implications much closer to home. Because diamond capsules are used in fusion experiments at Lawrence Livermore's National Ignition Facility, the researchers say their findings suggest those targets could be compressed with a slower, gentler initial shock than previously thought. Their calculations indicate the approach might produce roughly three times as much fusion energy from the fuel inside a capsule. That would be a significant improvement, although the technology would still remain far from the engineering breakeven needed for a practical fusion power plant.