National Ignition Facility earns its name for a second time

Scientists at Lawrence Livermore National Laboratory pushed the world’s most energetic laser to spark fusion ignition for the second time, surpassing the energy yield it attained last December. The 30 July shot at the lab’s National Ignition Facility (NIF) yielded 3.88 megajoules of energy, with an uncertainty of 0.31 MJ, from the 2.05 MJ of laser energy deposited on the target, according to three sources who asked not to be named. That was about a 20% increase from the December shot , which produced 3.15 MJ of fusion energy.

Neither Lawrence Livermore nor the Department of Energy announced the outcome of the recent experiment. Even after the Financial Times reported the achievement on 6 August, the lab declined to reveal any details. “While analysis of those results is underway, we can confirm the experiment produced a higher yield than the December test,” a lab spokesperson said in a statement. “As is our standard practice, we plan on reporting those results at upcoming scientific conferences and in peer-reviewed publications.”

Like the widely celebrated December experiment, the recent shot used a peppercorn-sized fuel capsule that was coated with nanocrystalline diamond by both Diamond Materials in Freiburg, Germany, and Lawrence Livermore. The diamond encapsulates a frozen mixture of deuterium and tritium. In several previous experiments performed earlier in the year, researchers had deliberately zapped capsules known to be of lower quality in order to better understand failure mechanisms. The 30 July shot was from a new batch, sources said.

When NIF’s 192 UV beams strike the inside of a small cylindrical chamber called a hohlraum, they emit x rays that cause the surface of the capsule inside to blow off like a rocket, uniformly imploding the fuel to a density and temperature sufficient to initiate fusion. The 14–15 keV plasma temperature that was measured during the latest shot also set a record.

NIF’s indirect drive approach is highly inefficient, and the fusion yields of both ignition-achieving experiments were puny compared with the 300 MJ of electricity needed to power the NIF laser. In addition, energy losses occur during the conversion of UV to x rays. Ultimately, only about 250 kJ reaches each capsule.

Another large DOE-supported laser, located at the University of Rochester’s Laboratory for Laser Energetics, focuses its energy directly onto fuel capsules. But that facility, known as Omega, is much too small to approach ignition conditions. Most of the private-sector inertial fusion energy hopefuls are planning to take a direct-drive approach, which in theory is far more efficient than NIF’s.

The $3.5 billion NIF was expected to reach ignition soon after its completion in 2009, but it wasn’t until 2021 that it got even halfway to that threshold. The laser has been used to perform other high-density physics and materials-science investigations that are relevant to the US nuclear weapons program.

The next shot with deuterium–tritium fuel is scheduled for 4 September, an experiment in support of the nuclear stockpile.