The major advance in fusion research announced in Washington on Tuesday was decades in coming, with scientists for the first time able to engineer a reaction that produced more power than was used to ignite it.

Using powerful lasers to focus enormous energy on a miniature capsule half the size of a BB, scientists at the Lawrence Livermore National Laboratory in California started a reaction that produced about 1.5 times more energy than was contained in the light used to produce it.

There are decades more to wait before fusion could one day — maybe — be used to produce electricity in the real world. But the promise of fusion is enticing. If harnessed, it could produce nearly limitless, carbon-free energy to supply humanity’s electricity needs without raising global temperatures and worsening climate change.

At the press conference in Washington, the scientists celebrated.

“So, this is pretty cool,” said Marvin “Marv” Adams, the National Nuclear Security Administration deputy administrator for defence programs.

“Fusion fuel in the capsule got squeezed, fusion reactions started. This had all happened before — 100 times before — but last week for the first time they designed this experiment so that the fusion fuel stayed hot enough, dense enough and round enough for long enough that it ignited,” said Adams. “And it produced more energy than the lasers had deposited.”

Here’s a look at exactly what nuclear fusion is, and some of the difficulties in turning it into the cheap and carbon-free energy source that scientists hope it can be.


Look up, and it’s happening right above you — nuclear fusion reactions power the sun and other stars.

The major advance in fusion research announced in Washington on Tuesday was decades in coming, with scientists for the first time able to engineer a reaction that produced more power than was used to ignite it.

The reaction happens when two light nuclei merge to form a single heavier nucleus. Because the total mass of that single nucleus is less than the mass of the two original nuclei, the leftover mass is energy that is released in the process, according to the Department of Energy.

In the case of the sun, its intense heat — millions of degrees Celsius — and the pressure exerted by its gravity allow atoms that would otherwise repel each other to fuse.

Scientists have long understood how nuclear fusion has worked and have been trying to duplicate the process on Earth as far back as the 1930s. Current efforts focus on fusing a pair of hydrogen isotopes — deuterium and tritium — according to the Department of Energy, which says that particular combination releases “much more energy than most fusion reactions” and requires less heat to do so.


Daniel Kammen, a professor of energy and society at the University of California at Berkeley, said nuclear fusion offers the possibility of “basically unlimited” fuel if the technology can be made commercially viable. The elements needed are available in seawater.

It’s also a process that doesn’t produce the radioactive waste of nuclear fission, Kammen said.

Crossing the line of net energy gain marks a major achievement, said Carolyn Kuranz, a University of Michigan professor and experimental plasma physicist.

“Of course, now people are thinking, well, how do we go to 10 times more or 100 times more? There’s always some next step,” Kuranz said. “But I think that’s a clear line of, yes, we have achieved ignition in the laboratory.”


One way scientists have tried to recreate nuclear fusion involves what’s called a tokamak — a doughnut-shaped vacuum chamber that uses powerful magnets to turn fuel into a superheated plasma (between 150 million and 300 million degrees Celsius) where fusion may occur.

The Livermore lab uses a different technique, with researchers firing a 192-beam laser at a small capsule filled with deuterium-tritium fuel. The lab reported that an August 2021 test produced 1.35 megajoules of fusion energy — about 70 per cent of the energy fired at the target. The lab said several subsequent experiments showed declining results, but researchers believed they had identified ways to improve the quality of the fuel capsule and the lasers’ symmetry.


It takes more than extreme heat and pressure. It also takes precision. The energy from the lasers must be applied precisely to counteract the outward force of the fusion fuel, according to Stephanie Diem, an engineering physics professor at the University of Wisconsin–Madison.

And that’s just to prove net energy gain is possible. It’s even harder to produce electricity in a power plant.

For example, the lab’s lasers can only fire a few times a day. To viably produce energy, they would need to fire rapidly and capsules would need to be inserted multiple times a minute, or even faster, Kuranz said.

Another challenge is to increase efficiency, said Jeremy Chittenden, a professor at Imperial College in London specializing in plasma physics. The lasers used at Livermore require a lot of electrical energy, and researchers need to figure out a way to reproduce their results in a much more cost-effective way, he said.

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There has been even more hype than usual about this latest small step forward in fusion research. Maybe this option has some future mileage, but if so then not for a very long time to come, and we have more important things to achieve now in the form of a rapid energy transition to renewables.

As noted somewhat obliquely in the article, the "net energy gain" does not take into account the energy input to the (apparently very inefficiency) lasers; nor does it take into account the energy required to create the "target" (electrolyse water; then separate out the deuterium and tritium, ensuring they are mixed in the correct ratio, which probably means some neutron bombardment to produce more tritium). And it's not a continuous process - once that globule of D-T plasma is used up, it's used up, so you need a stream of globules, which will change the geometry that the lasers have to compress.

Clean energy game-changer? I'm not holding my breath. Let's put our focus on the game-changing that we have to achieve now, at unprecedented speed but with real existing technologies.

Yeah. Also, far as I can tell, the "net energy gain" means how much energy the little capsule PRODUCED, not how much energy could plausibly be grabbed from it and turned into electricity. It's unlikely that the efficiency of turning little explosions into usable energy is going to be very high.

Side note, fusion is still going to create some radioactive waste, just not the same way fission does. Those little explosions, or the plasma in a tokamak reactor, are sending energetic particles all over the place, which are going to hit whatever's nearby (usually concrete shielding) and bust up some of its atoms, gradually making it radioactive. Eventually you're going to have a bunch of radioactive shielding to figure out what to do with. It's probably not as bad news as fission's spent fuel, but it's not zero byproducts.

I love fusion. Fusion is cool.
But. By the time fusion is a workable power source, either climate change will have been solved or civilization will have already fallen. Either way, we won't be getting power from fossil fuels. Fusion isn't going to be solving anything related to climate change.

Very exciting advance in science and engineering. Let's just not get distracted from the problem at hand which is to reduce greenhouse gas emissions to zero by 2050, preferably long before. Commercial energy production from nuclear fusion won't be available for decades, if ever. Even the scientists involved are not promising anything sooner.

I don’t want to downplay this achievement but it simply a waypoint on the route to a practical economic fusion reactor which, as it has been for seven decades, is many decades in the future.

Now to some rough numbers. We pay about ten cents per kilowatt-hour for electricity. That is 3.6 megajoules, say twice the output of energy from one pulse. Can a deuterium-tritium pellet be made for five cents? Not a chance. In the foreseeable future? No.

I agree with the previous commenter.