Friday, February 29, 2008

Big Science

Popular Mechanics has an article on how fusion research ought to be done.

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.
Now contrast that with another lab doing similar work. Five people. Total.

And what does the MIT Lab predict the outcome of their experiments (if successful) will be?
But even ITER, which is scheduled to be built within 8 to 10 years, is intended as a research facility—not as an answer to our current energy dilemma. It might produce an overall surplus of energy, but it won’t be cost-effective production. For that, Porkolab estimates we’ll have to wait for ITER to show results, possibly in the 2020s, and then wait another decade or so while demo reactors are built. That means we’d see economically feasible fusion power by 2035, at the earliest, and increasingly efficient commercial reactors somewhere in the middle of the century.

Even that protracted timeline now appears optimistic. Since 2006, when seven member countries committed to the ITER’s $10 billion budget, federal funding for scientific research in the United States appears to have bottomed out. The U.S. agreed to pay 9.1 percent of the project’s total cost—but of the $160 million contribution planned for this year, Congress has approved just $10.7 million. Porkolab says eight ITER engineers had been laid off without severance pay.
Now contrast that with the WB-7 project. They expect to complete their second round of experiments (the first were done on WB-6 in 2005) in the next 2 to 5 months. The cost to the US Navy? $1.8 million for WB-7 experiments.

If those experiments are successful they expect to have a net power test machine built within 5 years at a cost of about $40 million a year (average). It sure beats waiting until the 2020s to see results.

So what is wrong with the tokamak design? I'll let the MIT guys speak for themselves:
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.
Essentially the tokamak is a fight with nature. Nature wants to do one thing the scientists want it to do something else.

Contrast that with the Bussard Fusion Reactor. The design is one where instead of fighting natural tendencies it takes advantage of them.

In any case we will know a lot more in a few months. I'm keeping my fingers crossed.

No comments: