“People have been thinking about doing this for a long time, but the results were always inconclusive,” says Marmar. He says that the key to the MIT group’s success with radio waves was its development of more-effective methods for monitoring the plasma. “Most of the time, [physicists] do the measurements using the same neutral beams used to drive flow,” says Marmar. The MIT group tracks the flow of its plasma by introducing impurities that it can monitor using x-ray spectroscopy.
Wayne Houlberg, a scientist in the Fusion Science and Technology Department at ITER, believes that the MIT group’s work is interesting but still in its early stages. “Its applicability to the plasma conditions we expect in ITER will take time to evaluate,” he says.
MIT’s reactor is currently down for maintenance; running these experiments is so complex and expensive that reactors like MIT’s typically run for only three to four months a year. When experiments start up again, says Rice, he and his colleagues will work on fine-tuning the use of radio waves for controlling the plasma. “Ultimately, you’d like to control the shape of the rotation,” he says. For example, it might be better for the plasma in the center than for the plasma at the edges to rotate more quickly, or vice versa.
Practical fusion power plants are still decades away. In addition to confronting technological and scientific hurdles, fusion researchers have seen their funding stagnate. This year, the United States was to have significantly increased its financial support of ITER; the measure didn’t pass Congress. “We never know for sure what our budget will be,” says Marmar. “ITER is our best hope, but funding is caught in limbo.”