Levitating Magnet May Yield New Approach
to Clean Energy
Achieving nuclear fusion in the laboratory has been a cherished goal of physicists and energy researchers for more than 50 years. That’s because it offers the possibility of nearly endless supplies of energy with no carbon emissions and far less radioactive waste than that produced by today’s nuclear plants, which are based on fission, the splitting of atoms (the opposite of fusion, which involves fusing two atoms together). But developing a fusion reactor that produces a net output of energy has proved to be more challenging than initially thought.
|The Levitated Dipole Experiment (LDX) reactor, on the campus of MIT
Image credit: The LDX team
In findings published this week in the journal Nature Physics, a team at Columbia University and the Massachusetts Institute of Technology (MIT) reports on a unique approach that may allow scientists to generate clean energy from fusion.
“Fusion energy could provide a long-term solution to the planet’s energy needs without contributing to global warming,” said Michael E. Mauel, professor of applied physics at Columbia’s Fu Foundation School of Engineering and Applied Science.
The new results come from an experimental device, inspired by observations from space made by satellites. Called the Levitated Dipole Experiment, or LDX, a joint project of MIT and Columbia University, it uses a half-ton donut-shaped magnet about the size and shape of a large truck tire, made of superconducting wire coiled inside a stainless steel vessel. This magnet is suspended by a powerful electromagnetic field, and is used to control the motion of the 10-million-degree-hot electrically charged gas, or plasma, contained within its 16-foot-diameter outer chamber.
The results confirm the prediction that inside the device’s magnetic chamber, random turbulence causes the plasma to become more densely concentrated—a crucial step to getting atoms to fuse together—instead of becoming more spread out, as usually happens with turbulence. This “turbulent pinching” of the plasma has been observed in the way plasmas in space interact with the Earth’s and Jupiter’s magnetic fields, but has never before been recreated in the laboratory.
“It’s the first experiment of its kind,” said MIT senior scientist Jay Kesner, MIT’s physics research group leader for LDX, who co-directs the project with Mauel.
The results of the experiment show that this approach “could produce an alternative path to fusion,” Kesner said, though more research will be needed to determine whether it would be practical.
The whole concept, he said, was inspired by observations of planetary magnetic fields made by interplanetary spacecraft. In turn, he said, for planetary research the experiments in LDX can yield “a lot more subtle detail than you can get by launching satellites, and more cheaply.”
The MIT and Columbia scientists say that if the turbulence-induced density enhancement exhibited by the LDX could be scaled up to larger devices, it might enable them to recreate the conditions necessary to sustain fusion reactions, and thus may point the way toward abundant and sustainable production of fusion energy.
The LDX project, housed on the MIT campus and funded by the U.S. Department of Energy, has been through more than 10 years of design, construction and testing, and produced its first experimental results in its levitated configuration last year, which are being reported in the analysis published this week. Darren Garnier, a research scientist at Columbia who directs the project's experimental operations, last month received the Rose Award for Excellence in Fusion Engineering for his work on LDX.
“LDX is one of the most novel fusion plasma physics experiments underway today,” said Stewart Prager, director of the Princeton Plasma Physics Laboratory. Because of the unique geometry of the system, he says, “theoretical predictions indicate that the confinement of energy might be very favorable” for producing practical fusion power, but the theory needs to be confirmed in practice. “For these benefits to be realized, the somewhat bold theoretical predictions must be realized experimentally,” he said.
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