In 2023, energy from nuclear fusion — where two nuclei combine to form a new nucleus and release a ton of energy — became the topic du jour among some very influential people. Just weeks before COP28, the world’s preeminent climate conference, International Atomic Energy Agency Director General Rafael Mariano Grossi said of fusion, “For the first time, all the pieces of the puzzle are there: the physics, the policy drivers, and the investment.” His enthusiasm was matched at COP28 when John Kerry announced a call to action for engagement on fusion energy, and a host of panels circled in on the topic. This for a technology generally accepted even a few years ago to be “not what they’re cracked up to be.” So what changed? Evidence, that’s what.
A year ago, the National Ignition Facility (NIF) accomplished a goal decades in the making: The California-based site sparked a fusion reaction that generated more energy than it put in. Over the past year, NIF has repeated its energy gain achievement multiple times. Other fusion facilities are helping scientists plan for even bigger experiments to come. And, in many ways, planning for fusion power plants has already begun.
Combined, these advances have given fusion scientists reason to be more optimistic than ever. “For me… it’s this momentum that we feel everywhere in the world at the moment, towards a fusion power plant,” says Joëlle Mailloux, fusion scientist at the U.K. Atomic Energy Agency. She is not alone in this thinking.
The Name of the Gain
Fusion scientists often speak of a number called “gain,” which they mark with the letter Q. Gain, put simply, is the ratio of a fusion reaction’s output to the external energy that enters the reaction. In other words, a gain of more than 1 means you have created energy. NIF’s December 2022 shot achieved a gain of 1.5.
The magnitude of NIF’s achievement is difficult to understate: Fusion scientists have been fruitlessly chasing a gain of 1 since the 1950s. Not only did NIF surpass that threshold, but it also created a self-heating reaction that could keep burning without any additional external energy.
But if you want to tap fusion as a power source, you need to repeat these gains — something NIF had actually achieved four times as of November, according to Tom Arsenlis, a scientist at NIF. “While these experiments have not been exact repeats, we have demonstrated that we can robustly attain target gain greater than 1 and have some understanding as to the robustness of our design, fabrication, and fielding of the system,” Arsenlis says.
When you get into the nitty gritty, the painstaking difficulty of this feat starts to become clear. NIF relies on a technique called inertial confinement fusion (ICF). It works like this: A battery of lasers strikes a capsule stuffed with a hydrogen fuel pellet; the lasers create a cascade of X-rays inside the capsule, compressing the pellet into fusion. ICF is an extremely delicate procedure, and tiny tweaks to anything from the lasers’ angles to the pellet’s shape — changes that are often outside scientists’ control — can cause an experiment’s results to vary from shot to shot. No pain, no gain.
Cage Match: The Race for the Next Reaction
While the NIF is grabbing headlines, the Joint European Torus (JET) in England, which achieved a Q of 0.67 all the way back in 1998, sees an opening to take the prize.
Both JET’s technology and its technique differ from NIF’s — and are pushing the race to fusion from an entirely different angle. JET is an example of magnetic confinement fusion: an attempt to literally emulate the sun by creating a superheated magnetic plasma within a vacuum-sealed magnetic cage. More specifically, JET is a tokamak, a cage shaped like a doughnut.
For JET, 2023 will mark the passing of a torch. After more than 30 years of operation, the venerable old tokamak will fire its last plasma later this year. Scientists and engineers are now preparing to decommission the machine.
Picking up JET’s torch is Japan’s newly upgraded JT-60SA, now the world’s largest tokamak. JT-60SA won’t be ready for cutting-edge science until 2025, but the reactor achieved its first fusion this year. “In terms of physics results, it’s just a proof of principle that the machine operates,” says Joseph Snipes, a tokamak scientist at Princeton Plasma Physics Laboratory, a facility on Princeton University’s campus but run by the Department of Energy. “But that’s actually pretty normal for these big machines.”
“This is going to be the new flagship of the European program,” says Sara Moradi, deputy head of fusion science at EuroFusion, a pan-European consortium of fusion researchers. “It’s going to be the largest [tokamak] machine in the world for some time.”
Tokamaks are no easier — nor necessarily more difficult — to master than ICF. We know that they can reliably fuse atoms, but scientists still need to address a host of issues. A tokamak must hold turbulent, disruption-prone plasma in place for minutes on end. That plasma must be hot enough to create fusion, but its edges can’t be too hot, or they’ll scorch their chamber walls. Ideally, the plasma should fuse deuterium and tritium: heavier isotopes of hydrogen that make fusion more efficient.
To solve these problems, Tokamak scientists continue to work with other reactors, like Hefei, China’s EAST — which has set records by holding fusion — and California’s DIII-D. Neither these tokamaks nor JT-60SA will likely surpass a Q of 1 in themselves, but they are helping scientists prepare for a future machine that does.
For instance, as JT-60SA steadily comes online, its operators will thoroughly test each system and subsystem — and show scientists and technicians how to do it. “Maybe it’s not the sexiest part of starting up a reactor, but this is actually a very important part of any new machine that comes online,” says Morati. “This is, for us, an exciting period.”
Not all magnetic facilities are doughnut-shaped. Take the stellarator, a twisty-shaped reactor, popular in fusion’s early days of the 1950s and 1960s before it fell out of favor. But earlier this year, Wendelstein-7X, a research stellarator in Germany, sustained plasma for a landmark eight minutes. Not bad for a vintage cage.
Working Together on the Next Big Leap
It is true that the magnetic confinement world has not had a banner experiment along the lines of NIF, but those who work on the technology are hopeful. “We think [NIF’s] results are fantastic — we think they’re extremely interesting and promising for fusion,” says Ambrogio Fasoli, chair of EuroFusion’s general assembly. “But we maintain that our approach in magnetic fusion is probably the closest to a power plant, as of today.”
The next big leap in their master plan is the International Thermonuclear Experimental Reactor (ITER), now under construction in the south of France. ITER is, in one sense, fusion’s version of the International Space Station; it’s an international collaboration among countries from Europe, Asia, and North America.
No one has ever tried to build something like ITER before, and as with any megaproject, ITER has run into plenty of issues — the latest involving trouble assembling its chamber walls. But when ITER becomes fully operational, it will seek a gain of around 10, far eclipsing anything NIF has done.
ITER’s operators have no illusions that they’ll be the ones to create a commercial fusion power plant. Rather, they have planned ITER as a proof of concept that will let them practice for a fleet of future plants that they call DEMO. ITER’s current timeline has DEMO starting construction in the 2040s.
For those more impatient, a batch of startups and private-sector firms have mushroomed as of late — some promoting tokamaks, others toying with NIF-like lasers, and still others pushing stellarators — many promising fusion before this decade is even out.
Regardless of who builds the first working fusion power plant and when it starts up, the very first pieces of a fusion-powered world are already nearly in place. For instance, the U.K. and U.S. governments have begun to hammer out what the regulation and licensing schemes for fusion power plants look like.
Bureaucratic details may not be as flashy as the actual science, but the mere discussion itself excites scientists. “These are key developments,” says Mailloux.
