Last month, the US National Ignition Facility (NIF) fired its lasers up to full power for the first time since December, when it achieved its decades-long goal of ‘ignition’ by producing more energy during a nuclear reaction than it consumed. The latest run didn’t come close to matching up: NIF achieved only 4% of the output it did late last year. But scientists didn’t expect it to.

Building on NIF’s success, they are now flexing the programme’s experimental muscles, trying to better understand the nuclear-fusion facility’s capabilities. Here, Nature looks at what’s to come for NIF, and whether it will propel global efforts to create a vast supply of clean energy for the planet.

What was the goal of the latest experiment?

NIF, based at Lawrence Livermore National Laboratory (LLNL) in California, is a stadium-sized facility that fires 192 lasers at a tiny gold cylinder containing a diamond capsule. Inside the capsule sits a frozen pellet of the hydrogen isotopes deuterium and tritium. The lasers trigger an implosion, creating extreme heat and pressure that drive the hydrogen isotopes to fuse into helium, releasing additional energy.

One of the main challenges in getting this scheme to work is fabricating the diamond capsule. Even the smallest defects — bacterium-sized pockmarks, metal contamination or variations in shape and thickness — affect the implosion, and thus the pressure and heat that drive the fusion reactions.

Record-breaking experiments in 2021 and 2022 used the best capsules available, but in March, while waiting for a new batch, NIF scientists ran an experiment with a capsule that was thicker on one side than the other. Modelling suggested that they could offset this imperfection by adjusting the beams coming from the lasers, to produce a more uniform implosion. This was a test of their theoretical predictions, says Richard Town, a physicist who heads the lab’s inertial-confinement fusion science programme at the LLNL.

The results fell short of their predictions, and researchers are now working to understand why. But if this line of investigation pays off, Town says, “it opens up more capsules for us to use and will improve our understanding of implosion”.

What comes next at NIF?

Scientists succeeded in December by boosting the lasers’ energy and increasing the capsule thickness, which helps to prolong the fusion reactions. Experiments later this year will follow a similar strategy, says Annie Kritcher, a physicist who is leading the design of the campaign.

In the long term, the goal is to increase the amount of energy generated by fusion reactions from the 3.15 megajoules created last year to hundreds of megajoules. Town sees a viable path to increasing NIF’s energy yields to tens of megajoules by, among other things, further boosting the lasers’ energy going into the target. But he warns that NIF might soon need to make substantial safety upgrades: the facility is rated only for fusion yields of up to 45 megajoules. Before conducting any experiments that could approach that limit, the lab will need to, in strategic locations, reinforce the nearly 2-metre-thick concrete walls that contain the reaction.

How does this help the push to create fusion energy for the planet?

NIF was never designed to be a power plant. Its main goal was to help scientists verify that weapons in the US nuclear stockpile are reliable and safe by recreating and studying the reactions at their core. But hitting ignition in December “was a gateway event that opens the door for an energy programme”, says Stephen Dean, president of Fusion Power Associates, an advocacy group in Gaithersburg, Maryland.

The record-breaking experiment produced around 50% more energy than was delivered to the gold cylinder — and importantly, nearly 13 times the energy concentrated on the inner fuel pellet. For Max Karasik, a physicist at the Naval Research Laboratory in Washington DC, this highlights a potential path forward that he and others are pursuing: jettison the gold cylinder and focus the lasers directly on the fuel pellet, an experimental design known as direct drive.

In this configuration, “there is much more energy available for compressing the fuel pellet”, Karasik says.

But the challenges ahead for fusion energy are daunting. NIF’s lasers consumed 322 megajoules of energy in the landmark experiment in December. To deliver power to the public, Dean says, a laser-fusion plant would need to generate 100 times more energy than was input, and its lasers would need to fire around 10 times per second. This means designing a system that can accurately focus and fire the lasers on hundreds of thousands of targets each day.

With its current design, NIF will remain a place where scientists can learn from high-yield laser-fusion experiments, lab officials say. But in the meantime, private companies are increasingly stepping up with alternative solutions.

Last year, US President Joe Biden’s administration laid out its vision for a public–private partnership in fusion energy at a White House summit. The private sector will take the lead in pioneering new fusion technologies, while the US Department of Energy (DOE), of which NIF is a part, will advance knowledge in broader areas such as materials science, advanced manufacturing and modelling that will be crucial to commercialization.

Over the next 18 months, the DOE is looking to dole out US$50 million in grants to private fusion companies in a milestone-based programme modelled on NASA’s partnership with space-transport firms such as SpaceX. Laser-fusion companies will compete with firms pursuing other fusion designs, however. One of the most popular is the tokamak, a device that creates a magnetic field to contain the burning plasma generated by a fusion reaction in a doughnut-shaped ‘torus’. This is the approach being used by the world’s largest fusion experiment, ITER, in Saint-Paul-lès-Durance, France.

What are the odds of success?

The old joke about fusion energy is that it’s 50 years away, and always will be. Many scientists now say the front end of that equation is closer to 20–30 years, but it’s really just a matter of funding, says Pravesh Patel, a former scientist at Lawrence Livermore National Lab who currently serves as scientific director at Focused Energy in Austin, Texas, a private laser-fusion firm.

“As a scientist, I think fusion energy is inevitable,” he says. “The question is just how quickly we want it to work, and that depends on resources.”

This article is reproduced with permission and was first published on April 26, 2023.