Lawrence Livermore National Laboratory scientists on 14 August 2026 published a Nature Physics study that finally reconciles 20 years of contradictory diamond-melting data with quantum-mechanical simulations — and along the way opens a route to potentially tripling the energy gain of inertial confinement fusion shots at the National Ignition Facility (NIF).
Melting under Neptune-crushing pressure
Diamond is more than a gemstone. It is the material of the tiny fuel-capsule pellets crushed by NIF's 192 lasers to trigger fusion, and it may form as "diamond rain" deep inside Neptune and Uranus. Both scenarios push carbon to pressures three times greater than Earth's core. Until now, laboratory measurements of diamond's melting temperature disagreed with quantum-mechanics-based simulations by about 20 percent, and separate Sandia National Laboratories work using the Z machine suggested diamond might pass through an extra crystalline phase before melting.
The LLNL team, led by physicist Marius Millot and long-time collaborator Jon Eggert, ran laser-driven dynamic compression experiments at the Omega Laser Facility at the University of Rochester's Laboratory for Laser Energetics. Enhanced X-ray diffraction diagnostics let the scientists measure the atomic structure of diamond samples subjected to pressures higher than the centre of Neptune for just a billionth of a second.
Theory and experiment finally agree
The new measurements landed almost perfectly on the theoretical curve, closing the 20-year gap and confirming that diamond floats in metallic liquid carbon at high pressures — much like ice floats in water. The team also showed that under a single shock the sample stays in the diamond structure right up to melting, without the crystalline detour Sandia had inferred. The response depends on how the shock is applied, not just the temperature and pressure endpoint.
Softer shocks, bigger fusion gain
The result has an immediate implication for fusion. NIF experiments already use strong initial shocks to melt the diamond capsule uniformly, which is critical to avoid seeding implosion instabilities. The Nature Physics data indicates a slightly softer first shock can still fully melt the capsule while keeping the fuel more compressible — a change that models suggest could triple energy yield with the same laser energy, if other degradation pathways are held in check.
Bigger picture
The publication follows LLNL's Type One Energy cryogenic-pellet fueling licensing deal earlier this month and adds fresh momentum to the wider fusion trade, from Commonwealth Fusion's $1B raise for SPARC and ARC. It also feeds planetary science: because the experiments exceeded interior pressures of Neptune and Uranus, they refine models of "diamond rain" and ice-giant evolution.
Reporting based on coverage from Lawrence Livermore National Laboratory, Nature Physics, Interesting Engineering, ScienceAlert and Phys.org.