

The DOE defunded MIT’s Alcator C-Mod tokamak reactor back in 2012, and the university’s budget committee put it on the chopping block in 2013 and 2014. But advocates kept it ticking along until the end of September 2016. Now the 23-year-old fusion reactor has shut down for good — but not before the C-Mod team went for it one last time.

With nothing to lose, the team decided to push the reactor to the redline. “We’ve learned new things… and we haven’t broken the machine,” team lead Earl Marmar had told the MIT news in the last days of September. “It’s not over yet.”

The result of their efforts? A new world record in plasma pressure, double the best anyone outside of MIT has ever done, and achieved on C-Mod’s very last day of operation. By the numbers, the record-breaking run achieved 2.05 atmospheres at T > 35 million degrees Celsius. The team ran 1.4 million amps through C-Mod’s magnetic bottle, producing 300 trillion fusion reactions per second inside it while drawing some 4 megawatts. And then, with no further ado, the tokamak powered down.

The team presented their results at the IAEA’s Fusion Energy Conference in Kyoto yesterday (October 17th), and they aren’t necessarily scrapping the equipment. No sense in depriving future engineers, tinkerers, and other thinkers of whatever they can wring out of the decommissioned fusion reactor.

The problem that the C-Mod team was trying to solve is the same one that has to be solved before fusion will become viable: making it energy-positive on the surface of the earth. To get two nuclei to fuse, you have to overcome the Coulomb barrier: You have to mash the atoms together close enough that their mutual separation falls within the effective radius of the strong force holding each individual nucleus together. Manage this, and with a mighty release of energy, two atoms become one.

The trouble with this is that it’s expensive, in terms of upfront energy demand. 4 megawatts is a lot. While fusion is at the heart of the sun’s power output, the sun was sort of running before we got here, so the startup costs just aren’t the same. Here on earth, fusion seems to require huge amounts of electricity and powerful containment fields, which is why we don’t really see fusion outside of bombs and stars.

ITER, the next-generation fusion reactor under construction in France, will be almost 800 times larger than C-Mod. But it isn’t set to come online until 2027, so C-Mod’s record will probably stand for a while.

The easy joke is that fusion is the power source of the future, and always will be. Fuel for fusion is plentiful; hydrogen is basically everywhere. But until we can get over the Coulomb barrier, fusion as a domestic energy source will remain in the future.

MIT News says scientists, students, and faculty from the Alcator C-Mod team will discuss fusion power and the pressure record at an Ask Me Anything session on Reddit Thursday, Oct. 20, at 1 p.m. EDT.

Now read: How does fusion power ‘work,’ and will it ever be viable?