Neon gives healthy glow to reactor

Doughnut-shaped magnetic-fusion reactors known as tokamaks routinely reach the enormous temperature and density needed to fuse nuclei of hydrogen atoms. However, eddies in the fuel—a gas of hydrogen ions and electrons known as a plasma—spirit the energy away from the heart of the fusion furnace too quickly for a sustained reaction to take hold. Largely because of such turbulence, no fusion reactor has so far produced more energy than it has consumed, scientists say.

For decades, researchers have seen hints that impurities in fuel appear to boost performance of tokamaks. Now, a research team at the DIII-D National Fusion Facility operated by General Atomics in San Diego, Calif., (SN: 5/22/99, p. 327) has demonstrated that puffs of neon gas added to the fuel help hold the energy in the reactor’s center. Furthermore, the researchers showed that the technique achieved its effect in part by encouraging plasma flows that break up eddies.

The new results are “very exciting from several standpoints,” says George R. McKee of the University of Wisconsin-Madison. In the Feb. 28 Physical Review Letters, he and his colleagues present data showing a steep drop in turbulence when neon is in the reactor. By one measure, turbulence fell to a fifth of what it was without the gas.

Its tumble caused ion temperatures to double, McKee says. Neon’s presence also makes the plasma less damaging than usual to the reactor’s interior walls, he notes.

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