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Fusion project faces axe

Princeton stellarator threatened with closure.

A major US experiment that might open a more commercially attractive route to fusion is facing the prospect of closure after running into heavy cost overruns and scheduling delays.

On 15 September, a panel of independent scientists travelled to Princeton Plasma Physics Laboratory in New Jersey to determine whether to shut down the National Compact Stellarator Experiment (NCSX). Raymond Orbach, the Department of Energy's undersecretary for science, called for the review after discovering that the project was nearly US$40 million over budget and two years behind schedule. ?Given the magnitude of the increases projected,? Orbach wrote in a 9 August letter to the panel, ?all options, including termination of the project, must be considered.?

Japan's fusion machine, the Large Helical Device, has produced impressive results. Credit: NIFS, JAPAN

Whereas nuclear fission derives its energy from the splitting of heavy nuclei such as uranium, fusion produces energy from the fusing of lightweight elements, usually hydrogen isotopes. The dream is to produce energy from abundant materials such as sea-water without generating long-lived radioactive waste. Most of the world's current efforts to show that fusion could be a feasible energy option is focused on ITER, a massive reactor now under construction in Cadarache, France, and slated to cost $6 billion in construction and $6 billion in operating costs until 2026. (See box)

Fusion only takes place when hydrogen is heated to hundreds of millions of degrees to form a plasma, and so fusion reactors must contain their hydrogen fuel inside a magnetic field. ITER's design, known as a tokamak, will generate that field by a combination of external superconducting magnets and an internal current through the core (see Nature 436, 318; 2005). This design is relatively simple to build, but the internal current can disrupt the confinement.

The Princeton experiment hopes to get round those problems using an alternative set-up called a stellarator. Unlike tokamaks, stellarators use only external magnets to confine the plasma. The lack of an internal current makes the plasma more stable and, in theory at least, allows stellarators to run for longer than tokamaks. Stellarators cannot yet operate at the temperatures and pressures of tokamaks, but the results of early experiments are impressive: a Japanese stellarator known as the Large Helical Device, in Toki City, has held its plasma for more than an hour. Current tokamaks, by contrast, can hold their plasmas for a few minutes at most.

But the promise of stability comes at a cost, says Thomas Klinger of the Max Planck Institute for Plasma Physics in Greifswald, Germany. To hold plasma without an internal current requires much more complex magnetic-field geometry. That must be created with unusually shaped magnetic coils, which are difficult to manufacture. ?A stellarator is much simpler to operate, but much more difficult to build,? he says.

Construction seems to be at the core of the NCSX's woes. The project was originally budgeted at about $92 million with completion in 2009, but a review this July found that costs had ballooned to $130 million and completion date had been pushed back to 2011. ?As we came into the assembly phase, it turned out to be more complicated than we anticipated,? says Stewart Smith, dean of research at Princeton University, which oversees the lab and the experiment. Smith declined to comment further on the reasons for the delay, except to say that the cost underestimation was being taken ?very seriously?.

The review of the NCSX comes at a crucial time for the US fusion programme, according to Stephen Dean, the head of Fusion Power Associates, a non-profit group in Washington, Seattle, that advocates the development of fusion. The fusion-research community has long feared that US participation in ITER would starve other programmes of funds. As all planned fusion budget increases are to go towards the American contribution to ITER, that leaves no contingency for cost overruns in other programmes such as the NCSX, says Dean. ?I think there's a fair possibility that the Department of Energy will cancel the programme,? he says.

?In my opinion, that would be a sin,? says Klinger, who heads Wendelstein 7-X, a ?300-million ($416 million) German stellarator project under construction in Greifswald. Unlike the German reactor, the NCSX was to use a unique hybrid of stellarator and tokamak technology. If it worked, Klinger says, it could lead to tokamaks that could operate continuously, which would be far more commercially attractive than the ITER design. ?It is a very important experiment,? he says.

The fate of the programme will probably be determined after the current review is completed. The committee is expected to deliver its report at the end of October.


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Brumfiel, G. Fusion project faces axe. Nature 449, 265 (2007).

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