[Editors] MIT: new insights on fusion power

[Elizabeth Thomson]

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MIT: new insights on fusion power
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For Immediate Release
WEDNESDAY, DEC. 3, 2008

Contact: Elizabeth A. Thomson, MIT News Office
E: thomson at mit.edu, T: 617-258-5402

Photo Available

CAMBRIDGE, Mass.--Research carried out at MIT’s Alcator C-Mod fusion  
reactor may have brought the promise of fusion as a future power  
source a bit closer to reality, though scientists caution that a  
practical fusion powerplant is still decades away.

Fusion, the reaction that produces the sun’s energy, is thought to  
have enormous potential for future power generation because fusion  
plant operation produces no emissions, fuel sources are potentially  
abundant, and it produces relatively little (and short-lived)  
radioactive waste. But it still faces great hurdles.

“There’s been a lot of progress,” says physicist Earl Marmar, division  
head of the Alcator Project at the MIT Plasma Science and Fusion  
Center (PSFC). “We’re learning a lot more about the details of how  
these things work.”

The Alcator C-Mod reactor, in operation since 1993, has the highest  
magnetic field and the highest plasma pressure of any fusion reactor  
in the world, and is the largest fusion reactor operated by any  
university.

One of the most vexing issues facing those trying to construct a  
fusion plant that produces more power than it consumes (something  
never achieved yet experimentally) is how to propel the hot plasma (an  
electrically charged gas) around inside the donut-shaped reactor  
chamber. This is necessary to keep it from losing its heat of millions  
of degrees to the cooler vessel walls. Now, the MIT scientists think  
they may have found a way.

Physicist Yijun Lin and principal research scientist John Rice have  
led experiments that demonstrate a very efficient method for using  
radio-frequency waves to push the plasma around inside the vessel, not  
only keeping it from losing heat to the walls but also preventing  
internal turbulence that can reduce the efficiency of fusion reactions.

“That’s very important,” Marmar says, because presently used  
techniques to push the plasma will not work in future, higher-power  
reactors such as the planned ITER (International Thermonuclear  
Experimental Reactor) now under construction in France, and so new  
methods must be found. “People have been trying to do this for  
decades,” he says.

Lin says that “some of these results are surprising to theorists,” and  
as yet there is no satisfying theoretical foundation for why it works  
as it does. But the experimental results so far show that the method  
works, which could be crucial to the success of ITER and future power- 
generating fusion reactors. Lack of a controllable mechanism for  
propelling the plasma around the reactor “is potentially a  
showstopper,” Rice says, and the ITER team is “very concerned about  
this.”

Rice adds that “we’ve been looking for this effect for many years,”  
trying different variations of fuel mixture, frequency of the radio  
waves, and other parameters. “Finally, the conditions were just  
right.” Given that the ITER project, which will take 10 years to  
build, is already underway, “our results are just in time for this,”  
Lin says. These results are being published in Physical Review Letters  
on Dec. 5. The work was sponsored by the US Department of Energy.

A number of other recent findings from Alcator C-Mod research could  
also play a significant role in making fusion practical, and several  
papers on these new results were presented at the Plasma Physics  
Divisional meeting of the American Physical Society held in November.

One of these is a method developed by Dennis Whyte and Robert Granetz  
for preventing a kind of runaway effect that could cause severe damage  
to reactor components. When a fusion reactor is in operation, any  
disruption of the magnetic field that confines the super-hot plasma  
could cause a very powerful beam of “runaway electrons,” with enough  
energy to melt through solid steel. This would not be dangerous to  
personnel because everything is well-shielded, but it could cause  
hardware damage that would be expensive and time-consuming to repair.

But Whyte and Granetz have developed a kind of high-powered fire  
extinguisher for such runaway beams: A way of suddenly injecting a  
blast of argon or neon gas into the reactor vessel that turns the  
plasma energy into light, which is then harmlessly absorbed by the  
reactor walls, and suppresses the beam by apparently making the  
magnetic fields more disorganized.

For about a thousandth of a second, Whyte says, this brilliant flash  
of light is the world’s brightest light — the equivalent of a billion- 
watt bulb — though it’s in a place where nobody can directly see it.

Because the Alcator C-Mod’s design is very closely matched to that of  
ITER, “we are uniquely positioned to explore what happens when these  
disruptions occur,” Whyte says. ITER will be 10 times the diameter,  
with a thousand times the energy, so if this quenching system is used  
there it would produce a trillion-watt bulb — for a fleeting instant,  
nearly equivalent to the total electricity output of the United States.


--END--

Written by David Chandler, MIT News Office
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