The US fusion energy breakthrough: Everything you need to know


On Tuesday, the Department of Energy is expected to announce a long-awaited milestone in the development of nuclear fusion energy: net energy gain. The news, first reported by the Financial Times and confirmed by The Washington Post, could galvanize the fusion community, which has long hyped the technology as a possible clean energy tool to combat climate change.

But how big of a deal is the “net energy gain” anyway — and what does it mean for the fusion power plants of the future? Here’s what you need to know.

Existing nuclear power plants work through fission — splitting apart heavy atoms to create energy. In fission, a neutron collides with a heavy uranium atom, splitting it into lighter atoms and releasing a lot of heat and energy at the same time.

Fusion, on the other hand, works in the opposite way — it involves smushing two atoms (often two hydrogen atoms) together to create a new element (often helium), in the same way that stars create energy. In that process, the two hydrogen atoms lose a small amount of mass, which is converted to energy according to Einstein’s famous equation, E=mc². Because the speed of light is very, very fast — 300,000,000 meters per second — even a tiny amount of mass lost can result in a ton of energy.

What is “net energy gain,” and how did the researchers achieve it?

Up to this point, researchers have been able to fuse two hydrogen atoms together successfully, but it’s always taken more energy to do the reaction than they get back. Net energy gain — where they get more energy back than they put in to create the reaction — has been the elusive holy grail of fusion research.

Now, researchers at the National Ignition Facility at the Lawrence Livermore National Laboratory in California are expected to announce that they have attained net energy gain by shooting lasers at hydrogen atoms. The 192 laser beams compress the hydrogen atoms down to about 100 times the density of lead and heat them to approximately 100 million degrees Celsius. The high density and temperature cause the atoms to merge into helium.

Other methods being researched involve using magnets to confine superhot plasma.

“If it’s what we’re expecting, it’s like the Kitty Hawk moment for the Wright brothers,” said Melanie Windridge, a plasma physicist and the CEO of Fusion Energy Insights. “It’s like the plane taking off.”

Does this mean fusion energy is ready for prime time?

No. Scientists refer to the current breakthrough as “scientific net energy gain” — meaning that more energy has come out of the reaction than was inputted by the laser. That’s a huge milestone that has never before been achieved.

But it’s only a net energy gain at the micro level. The lasers used at the Livermore lab are only about 1 percent efficient, according to Troy Carter, a plasma physicist at the University of California, Los Angeles. That means that it takes about 100 times more energy to run the lasers than they are ultimately able to deliver to the hydrogen atoms.

So researchers will still have to reach “engineering net energy gain,” or the point at which the entire process takes less energy than is outputted by the reaction. They will also have to figure out how to turn the outputted energy — currently in the form of kinetic energy from the helium nucleus and the neutron — into a form that is usable for electricity. They could do that by converting it to heat, then heating steam to turn a turbine and run a generator. That process also has efficiency limitations.

All that means that the energy gain will probably need to be pushed much, much higher for fusion to actually be commercially viable.

At the moment, researchers can also only do the fusion reaction about once a day. In between, they have to allow the lasers to cool down and replace the fusion fuel target. A commercially viable plant would need to be able to do it several times per second, says Dennis Whyte, director of the Plasma Science and Fusion Center at MIT. “Once you’ve got scientific viability,” he said, “you’ve got to figure out engineering viability.”

What are the benefits of fusion?

Fusion’s possibilities are enormous. The technology is much, much safer than nuclear fission, since fusion can’t create runaway reactions. It also doesn’t produce radioactive byproducts that need to be stored, or harmful carbon emissions; it simply produces inert helium and a neutron. And we’re not likely to run out of fuel: The fuel for fusion is just heavy hydrogen atoms, which can be found in seawater.

When could fusion actually power our homes?

That’s the trillion-dollar question. For decades, scientists have joked that fusion is always 30 or 40 years away; over the years, researchers have variously predicted that fusion plants will be operational in the 90s, the 2000s, the 2010s, and the 2020s. Current fusion experts argue that it’s not a matter of time, but a matter of will — if governments and private donors finance fusion aggressively, they say, a prototype fusion power plant could be available in the 2030s.

“The timeline is not really a question of time,” Carter said. “It’s a question of innovating and putting the effort in.”

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