IT ALWAYS seems to be 30 years away. Controlled nuclear fusion seems no closer to being realised now than it was when the idea was put forward in the 1950s. But fusion power stations might be closer than anyone suspected – if we think small.
Bigger is better, or so goes the accepted wisdom with nuclear fusion. The massive international experiment ITER takes this to the extreme, employing a doughnut-shaped reaction chamber 20 metres across and up to 1000 staff. The price tag? A mere $50 billion.
Now some are advocating that a smaller-scale approach could be swifter and cheaper. Last month, the aerospace firm Lockheed Martin claimed its compact fusion reactor design, small enough to hitch to a truck, could be ready in a decade. Tom Jarboe at the University of Washington in Seattle has developed his own small-scale reactor, which he says could cost less than $3 billion to get working within 15 years.
Fusion reactors promise cheap, clean energy, leaving behind only small amounts of radioactive waste and with little risk of runaway meltdowns. The reactors that ITER, Lockheed Martin and Jarboe are developing all use magnets to contain a mixture of deuterium and tritium (stable isotopes of hydrogen), heated to the point where electrons separate from the atomic nuclei. The magnetic fields squeeze this scorching hot plasma to force the nuclei together. That fuses them into helium nuclei, releasing neutrons and generating vast amounts of energy.
It is easier said than done. "Plasma physics isn't rocket science," Jarboe says as we look over the shiny tubes and curves of his latest reactor. "It's much, much harder."
A major challenge is how to hold the chaotic plasma in place for more than the tiniest fraction of a second. Reactors like the one at ITER try to do it using magnetic fields produced with the aid of coils around the doughnut and superconducting magnets running up through the central hole. But that requires metres of costly, bulky shielding to protect the chilled magnets from energetic neutrons.
Jarboe's approach shrinks things down using a so-called spheromak design, in which current from the flowing plasma generates a magnetic field that, elegantly, confines the plasma itself. With no sensitive components inside the hole, spheromaks can be as small as desired.
Spheromaks were in vogue in the 1970s when Jarboe began working on them at the Los Alamos National Laboratory in New Mexico, but back then they couldn't confine a hot plasma for longer than the blink of an eye. The car-sized experiment that Jarboe has working today is the first spheromak to confine high-pressure plasma. "It could go on indefinitely if we had the cooling and power supply," he says.
Jarboe is now seeking $8 million from the US Department of Energy to build a larger experiment that will reach the temperatures necessary to prove the technology.
Which design wins out may come down to funding. ITER's spiralling budget has siphoned off most of the money, and much of the enthusiasm, for fusion research in the US. If there is no money to fund some of the more promising alternative approaches, that 30-year horizon could remain a stubborn fixture for some time to come.
This article appeared in print under the headline "Road to fusion open to anyone of modest means"
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