We still don’t have energy-positive fusion yet, but MIT just got close
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.