MIT Fights for Clean Power With Holy Grail of Fusion in Reach
In the first part of a week-long series at the breakthrough university, our resident geek looks down the belly of extreme machines with forces some 100,000 times stronger than the Earth’s—and forecasts the future of efficient energy.
By Erik Sofge
Published on: February 25, 2008
MIT WEEK: OTHER ARTICLES IN THIS SERIES
• MONDAY: MIT Fights for Clean Power With Holy Grail of Fusion in Reach
CAMBRIDGE, Mass. — This is what a fusion lab is supposed to be like. As I walk in, a woman’s voice is on the speakers, counting down from 10. Banks of chairs face banks of computer monitors, where data is literally streaming across application windows that are pulsing, multicolored and reassuringly complex. And at the head of the control room is a massive projection showing a diagram of the fusion chamber nearby—a top-down view of the donut-shaped, concrete-lined structure that’s about to fill with superheated ionized gas, or plasma. On the same wall is looped footage of the last “shot,” a brief attempt to harness that plasma, and make fusion a little more feasible. The countdown is over, and there’s a sound straight out of sci-fi—a high tone coupled with a deep, resonating hum. On a tiny, black-and-white monitor mounted on the ceiling, a 1-second flash ripples across the screen. A sign lights up over the door leading to the chamber, indicating that the oxygen is too low for anyone to approach without breathing gear, and the clock starts again. Next shot in 15 minutes.
MIT’s Plasma Science and Fusion Center (PSFC) is about as Hollywood-worthy as science gets. The stakes, after all, could hardly be higher. If fusion can be perfected, it could mean a golden age for power production, with systems providing all of the benefits of nuclear reactors—but none of the drawbacks. Fusion is, to some extent, the exact opposite of fission: Instead of splitting atoms, fusion combines them, creating larger atoms and releasing a massive amount of energy in the process. Despite the high temperatures often associated with plasma, fusion is a relatively stable reaction, generating little to no radioactive waste. Even in a worst-case scenario, there’s no chance of a fusion reactor turning into a catastrophe on the scale of Three-Mile Island or Chernobyl. “Fission can run away,” says Miklos Porkolab, director of the PSFC. “Fusion can only fizzle.” Since there’s no chain reaction at work, the biggest danger associated with fusion is a temperature collapse. And even if the materials lining the chamber were to suddenly give way because of sabotage or terrorism, the introduction of debris into the plasma cloud would actually smother the process at an even faster rate. Fusion is fragile, difficult to maintain and ultimately its own worst enemy. But it is not dangerous.
That quality makes it utterly useless as a weapon, Porkolab explains, which is why the federal government decided to declassify its fusion research 50 years ago and make the results public. That was effectively the birth of open, academic fusion in the United States. So a half-century into this quest for one of science’s holy grails, are we any closer to grace?
The answer, not surprisingly, is mixed. Here at MIT, the fusion center’s primary research tool is the Alcator C-MOD, the largest university-run fusion reactor in the world, and one of only three “tokamaks” in the country. Tokamaks are reactors that use magnetic fields to control the flow of plasma. Extreme machines like the C-MOD, which has the most powerful magnetic fields of any tokamak (and some 100,000 times stronger than the Earth’s) have enhanced our understanding of fusion. But a truly efficient reaction, with more energy released than poured in, is still decades away.
The problem, Porkolab says, is turbulence. To increase the chances of a fusion reaction, a cloud of plasma must be incredibly hot and dense. As the atoms become more closely packed and excited, the natural tendency for nuclei to repel each other can be overcome. C-MOD uses microwaves to heat the ionized gas and magnets to shape it, building up pressure within the plasma. But as any meteorologist can tell you, juggling temperature and pressure is a recipe for bad weather. “We have our own storms, inside the plasma, just like in the atmosphere,” Porkolab says. Temperature gradients within the plasma can lead to eddies, and the more unstable the cloud becomes, the more heat it loses. When the temperature gets low enough, the reaction dies. Plasma turbulence, in other words, is the biggest obstacle to fusion, limiting current reactors to brief pulses and preventing the kind of long-term reaction necessary for true power production.
That’s why, when the next countdown begins in the control room, and I try to catch the real-time flash of the plasma shot on that tiny ceiling-mounted monitor, it’s gone before my camera can even focus. The replay starts to loop on the main screen—a slightly misleading bit of pyrotechnics, since the visible light released by the shot is generated at the edges of the plasma donut, where temperatures are at their lowest, and where fusion is not likely to occur. And while it’s possible that C-MOD’s pulses could one day last longer than seconds, this particular tokamak won’t reach the promised land. In many ways, C-MOD’s most important job is to pave the way for a reactor 10 times its size, called ITER.