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A Workable Fusion Reactor

Cutting fusion down to practical size.

It’s an old joke that many fusion scientists have grown tired of hearing: Practical nuclear fusion power is just 30 years away—and always will be.

But now, that may no longer be true. New advances in magnet technology have enabled researchers at MIT to propose a new design for a practical compact tokamak fusion reactor—and it’s one that might be realized in as little as a decade, they say.

The new reactor uses coils of rare-earth barium copper oxide, a commercially available superconductor, to generate an extremely strong magnetic field. Introducing this material “just ripples through the whole design,” says Dennis Whyte, a professor of nuclear science and engineering and director of MIT’s Plasma Science and Fusion Center. “It changes the whole thing.”

The stronger magnetic field makes it possible to confine the superhot plasma—the electrically charged gas that feeds the fusion reaction—within a much smaller device than those previously envisioned. The reduction in size, in turn, makes the whole system less expensive and faster to build. The reactor concept, which uses a tokamak (doughnut-shaped) geometry that is widely studied, was developed by Whyte, PhD candidate Brandon Sorbom, and several other students. Their concept originated in a design class taught by Whyte and continued as a student-led project after the class ended.

The new reactor is designed for basic research on fusion and also as a potential prototype power plant that could produce significant power. “The much higher magnetic field allows you to achieve much higher performance,” says Sorbom.

Fusion reactors, which rely on the same nuclear reaction that powers the sun, force pairs of hydrogen atoms together to form helium, which releases enormous amounts of energy. The hardest part of designing a workable reactor has been confining the plasma while heating it to temperatures hotter than the cores of stars. This is where the magnetic fields are critical: they effectively trap the heat and particles in the hot center of the device.

The new superconductors make it possible to increase the power produced by about a factor of 10 compared with standard superconducting technology, Sorbom says. Right now, he adds, the reactor should be capable of producing about three times as much electricity as is needed to keep it running. The design could probably be improved to increase that proportion to about five or six times, he says, which would yield enough electricity for about 100,000 people. Until now, no fusion reactor has produced as much energy as it consumes.

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