But how big a deal is “net energy gain” anyway – and what does it mean for future fusion power plants? Here’s what you need to know.
Existing nuclear power plants work through fission — split apart heavy atoms to create energy. In fission, a neutron collides with a heavy uranium atom, splitting it into lighter atoms and simultaneously releasing a lot of heat and energy.
Fusion, on the other hand, works in the opposite way – it involves smashing two atoms (often two hydrogen atoms) together to make 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 into 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 small 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, scientists have been able to fuse two hydrogen atoms together successfully, but it has always taken more energy to carry out 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 fusion research’s elusive holy grail.
Now scientists at the National Ignition Facility at Lawrence Livermore National Laboratory in California are expected to announce that they have achieved a net energy gain by firing lasers at hydrogen atoms. The 192 laser beams compress the hydrogen atoms down to about 100 times the density of lead and heat them up to about 100 million degrees Celsius. The high density and temperature cause the atoms to fuse together to form helium.
Other methods being researched involve the use of magnets to confine super-hot plasma.
“If it’s what we expect, it’s like the Kitty Hawk moment for the Wright brothers,” said Melanie Windridge, a plasma physicist and CEO of Fusion Energy Insights. “It’s like the plane is 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 supplied by the laser. It is a major milestone that has never been achieved before.
But it is 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 it takes about 100 times more energy to run the lasers than they are ultimately able to deliver to the hydrogen atoms.
So the researchers will still have to reach the “engineering net energy gain”, or the point where the entire process takes less energy than is produced by the reaction. They also need to figure out how to turn the emitted energy – currently in the form of kinetic energy from the helium nucleus and the neutron – into a form usable for electricity. They could do that by converting it to heat, then heating steam to turn a turbine and drive a generator. That process also has efficiency limitations.
All of this means that the energy gains will likely have to be pushed much, much higher for fusion to actually be commercially viable.
Currently, scientists can also only do the fusion reaction about once a day. In between, they have to let the lasers cool down and replace the fusion fuel target. A commercially viable plant must be able to do that 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 have to figure out technical viability.”
What are the advantages of fusion?
Fusion’s possibilities are enormous. The technology is much, much safer than nuclear fission, since fusion cannot create runaway reactions. It also does not produce radioactive by-products that need to be stored, or harmful carbon emissions; it simply produces inert helium and a neutron. And we probably won’t run out of fuel: the fusion fuel is just heavy hydrogen atoms, which are found in seawater.
When could fusion actually power our homes?
It’s the trillion dollar question. For decades, scientists have joked that fusion is always 30 or 40 years away; Over the years, scientists have variously predicted that fusion plants will be in operation in the 90s, 2000s, 2010s and 2020s. Current fusion experts argue that it’s not a matter of time, but a matter of will — if governments and private donors fund fusion aggressively, they say, a prototype fusion power plant could be available in the 2030s.
“The timeline isn’t really a matter of time,” Carter said. “It’s a matter of innovation and effort.”
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