NovaNext Raleigh McElvery on Mon, 17 Oct 2016
On Albany Street in Cambridge, Massachusetts, there is a device that confines the power of the stars, generating energy at over 180 million degrees F. Known as the Alcator C-Mod, MIT’s plasma fusion experiment has operated for more than 20 years. Yet as of Friday, September 30, it was terminated by federal decree.
Four years ago, without warning, the Department of Energy (DOE) announced its controversial decision to cut funding. Although the closure date was originally slated for October 2012, after some negotiation this timeline was ultimately pushed to the end of the 2016 federal fiscal year. “To this day, C-Mod is still a highly productive and unique plasma fusion experiment run by a number of outstanding scientists,” said Michael Mauel, professor of applied physics at Columbia University, who runs his own fusion experiment.
While it may sound like the stuff of fiction, plasma is simply a state of matter composed of charged particles. At temperatures as hot as the sun, the positively charged particles collide and fuse together, releasing energy in the form of heat. The particles move extremely quickly—so quickly they could travel around the Earth several times in a single second.
Scientists hope to one day construct fusion reactors capable of supplying nearly unlimited electricity. It would be the holy grail of energy production, since nuclear fusion generates very little radioactive waste and no greenhouse gasses. But first, scientists must learn how to trap the plasma in a container with magnetic fields for long periods of time, using less energy than the fusion process creates.
C-Mod is a container called a tokamak, which resembles a donut. The circular machine confines the plasma using immense magnetic forces, holding the whizzing particles in a ring for several seconds at a time. C-Mod boasts the highest magnetic field of any tokamak—40,000 times more powerful than the Earth’s own magnetic field—even though the device is fairly compact compared to the 200 others in existence. The donut’s radius is only about 67 cm.
Some attribute the DOE’s decision to C-Mod’s diminutive size. “It’s not as large or as new as many other machines, which do novel things with plasma C-Mod can no longer do,” said Dr. Weston Stacey, professor of nuclear engineering at Georgia Tech. “Its time has come.” Stacey said there are advantages to being big, because anything remotely resembling a reactor must be relatively large. “You don’t want to light a lightbulb, you want to light a city,” he said.
Others disagree. “I wouldn’t say small isn’t as good,” Mauel said. “Fusion requires a large product of magnetic strength and physical size. Because C-Mod has very high magnetic strength, it can operate at smaller size,” he added.
The DOE’s decision to shut down a working experiment was intended to shift funding to international efforts to achieve a self-heated plasma. “At the moment, that’s ITER,” Mauel said.
Started in 2006, ITER, the International Thermonuclear Experimental Reactor, is a 35-country collaboration that’s assembling the world’s largest fusion experiment in the south of France.
“ITER will weigh almost a thousand times as much as C-Mod and cost about a thousand times more to build,” said head of the C-Mod project, Dr. Earl Marmar. “When ITER was proposed, it was going to cost the U.S.—a 9% partner in the project—about $1.1 billion. Now, a recent DOE review suggests it’s between $3-6 billion.”
At MIT, C-Mod had been producing plasma for over 20 years. Marmar claims the DOE’s choice to cut funding was a political one. “ITER is promising to do something we were never designed to do because we would need a bigger facility,” he said.
To emulate a power plant, the MIT facility would need to be large enough to reach 360 million degrees F. “We think we can do that in the future,” Marmar said.
Since the DOE announced its decision in 2012, he’s had plenty of time to plan his next steps. His team at MIT hopes to eventually develop superior superconducting magnets for their next tokamak that will more effectively confine and heat the plasma.
On the C-Mod’s final day of operation, Marmar and his colleagues gave the tokamak one last hurrah, cranking up the pressure inside its powerful magnetic fields. At 9:25 pm, they had squeezed the 63 million degree F plasma to 2.05 atmospheres, twice as dense as air pressure at sea level, breaking their own record set back in 2005.
“We think we could make something not much more than twice as big as C-Mod that could put more power out than we would need to run the facility,” Marmar said. “At the moment though, we still don’t have funding.”