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Sunday, May 19, 2024

The Real Fusion Energy Breakthrough Is Still Decades Away

Last week, inside a gold-plated drum in a Northern California lab, a group of scientists briefly recreated the physics that power the sun. Their late-night experiment involved firing 192 lasers into the capsule, which contained a peppercorn-sized pellet filled with hydrogen atoms. Some of those atoms, which ordinarily repel, were smushed together and fused, a process that produces energy. By standards of Earth-bound fusion reactions, it was a lot of energy. For years, scientists have done this type of experiment only to see it fall short of the energy used to cook the fuel. This time, at long last, they exceeded it.

That feat, known as ignition, is a huge win for those who study fusion. Scientists have only had to gaze up at the stars to know that such a power source is possible—that combining two hydrogen atoms to produce one helium atom entails a loss of mass, and therefore, according to E = mc2, a release of energy. But it’s been a slow road since the 1970s, when scientists first defined the goal of ignition, also sometimes known as “breakeven.” Last year, researchers at the Lawrence Livermore Lab’s National Ignition Facility came close, generating about 70 percent of the laser energy they fired into the experiment. They pressed on with the experiments. Then, on December 5, just after 1 am, they finally took the perfect shot. Two megajoules in; 3 megajoules out. A 50 percent gain of energy. “This shows that it can be done,” said Jennifer Granholm, US Secretary of Energy, at a press conference earlier this morning.

To fusion scientists like Mark Cappelli, a physicist at Stanford University who wasn’t involved in the research, it’s a thrilling result. But he cautions that those pinning hopes on fusion as an abundant, carbon-free, and waste-free power source in the near future may be left waiting. The difference, he says, is in how scientists define breakeven. Today, the NIF researchers said they got as much energy out as their laser fired at the experiment—a massive, long-awaited achievement. But the problem is that the energy in those lasers represents a tiny fraction of the total power involved in firing up the lasers. By that measure, NIF is getting way less than it’s putting in. “That type of breakeven is way, way, way, way down the road,” Cappelli says. “That’s decades down the road. Maybe even a half-century down the road.”

The trouble is inefficient lasers. Generating fusion energy using NIF’s method involves shooting dozens of beams into a gold cylinder called a hohlraum, heating it up to more than 3 million degrees Celsius. The lasers don’t target the fuel directly. Instead, their aim is to generate “a soup of X-rays,” says Carolyn Kuranz, a fusion researcher at the University of Michigan. These bombard the tiny fuel pellet consisting of the hydrogen isotopes deuterium and tritium, and crush it.

This must be done with perfect symmetrical precision—a “stable implosion.” Otherwise, the pellet will wrinkle and the fuel won’t heat up enough. To achieve last week’s result, the NIF researchers used improved computer models to enhance the design of the capsule that holds the fuel and calibrate the laser beams to produce just the right X-ray dispersion.

Currently, those lasers emit about 2 megajoules of energy per pulse. To fusion scientists, that’s a massive, exciting amount of energy. It’s only equivalent to roughly the energy used in about 15 minutes of running a hair dryer—but delivered all at once, in a millionth of a second. Producing those beams at NIF involves a space nearly the size of a football field, filled with flashing lamps that excite the laser rods and propagate the beams. That alone takes 300 megajoules of energy, most of which is lost. Add to that layers of cooling systems and computers, and you quickly get an energy input that’s multiple orders of magnitude greater than the energy produced by fusion. So, step one for practical fusion, according to Cappelli, is using much more efficient lasers.

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The headaches continue on the other side of the energy equation, he adds. A conventional combustion engine is about 40 percent efficient at converting the energy it produces into electricity. For fusion, that might be more like 10 to 20 percent, he suggests. And researchers aren’t even close to thinking about that type of conversion. By definition, fusion experiments are exercises in destruction. The fuel pellet is designed to be crushed in one go; the surrounding instruments are destroyed by the release of fusion energy; the mirrors are damaged by the powerful lasers. So to produce sustained energy, scientists need to figure out how to repeatedly fire the powerful lasers and get many pellets in front of them. That could involve multiple pellets and laser firings per minute, Kuranz says. By comparison, NIF currently fires three times per day.

Still, the progress announced today is a big deal, she adds. An overlooked aspect of this type of fusion experiment, known as “inertial confinement,” is that lasers themselves are a relatively new technology—newer than technology like nuclear fission. “The multi-megajoule lasers we have today are an amazing engineering feat,” she says, compared with the lasers first developed in the 1960s. And the NIF researchers have done more with that energy than many people thought they could. Some thought that to get anywhere close to ignition, it might take 10 or more megajoules of laser energy. Plus, she adds, lasers have continued to improve in the decades since NIF broke ground in 1999, meaning tantalizing possibilities for the facilities that could someday replace it.

That’s exciting, she says, because in the past inertial confinement has gotten less attention than another type of fusion technology known as “magnetic confinement.” This involves a donut-shaped device known as a tokamak, in which hydrogen gas is heated into plasma and then trapped by magnetic fields. Commercial fusion companies have generally taken the magnet route, in part because of the challenges of lasers. But recently, inertial facilities have seen more investment—and today’s success may mean more of that ahead, Kuranz says. 

So will fusion help fix climate change? The Biden administration has high hopes, directing significant investment to fusion research through the Inflation Reduction Act. In April, it announced a 10-year vision for building toward commercial fusion. The actual timeline remains hazy, on the scale of “decades” (plural). But “with real energy and real focus, that timeline can move closer,” said Kimberly Budil, director of Lawrence Livermore National Lab, at today’s press conference.

Still, some find it a distraction from the path to achieving the US goal of net-zero energy production, given the tremendous costs. After all, if the goal is to do that by 2035, “decades” won’t cut it. “Despite today’s announcement, fusion is neither commercial nor close to commercial, so it is still vaporware,” says Mark Jacobson, an energy researcher at Stanford who has argued for more investment in available solutions like solar, wind, and hydropower. Indeed, you would be hard-pressed to find a plasma physicist who thinks fusion will be in the mix in the next decade. 

But for nearly a century, since astronomer Arthur Eddington speculated on the relationship of hydrogen and helium powering the sun, people have been attracted to the “what if” possibility of building a power plant that worked like a star. There’s an Icarian quality to it, of course, a humbling from decades of high expectations that are rarely met. But fusion researchers press on toward an elusive goal, even if it may not be attained by any generation alive today. “I think we should look at this with optimism,” says Dmitri Orlov, a research scientist at the University of California, San Diego who studies tokamak design. “Today is like watching a baby learning to walk. Eventually, it will run a marathon.”

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