It's Too Early to Pick a Winner on Inertial Fusion Energy, Says Study

Daniel is a deputy news editor for Science.

Despite proposed cuts to the U.S. magnetic fusion program, a new report advocates a parallel effort to pursue fusion energy using the rival inertial confinement scheme. The report, by the National Academies' National Research Council, says that it is too early to pick a winning technology and focus funding on that approach. That conclusion will please many scientists in the field who have been concerned that the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory—the world's largest and most advanced inertial fusion facility—was poised to dominate the U.S. research effort.

The NRC committee was convened at the request of Steven Koonin, who last fall stepped down as the Department of Energy's (DOE) undersecretary for science. NIF officials say that they are closing in on achieving "ignition"—a self-sustaining fusion reaction that generates at least as much energy as it consumes. Such a breakthrough would show that inertial fusion, at least in principle, is a possibility for future power stations. With that in mind, Koonin asked NRC to suggest DOE's next steps on the road to a demonstrator power reactor, including a road map of technology development. Today's release is an interim report from the committee.

Inertial fusion doesn't have a single home within DOE. All U.S. research in magnetic fusion is funded by the DOE's Office of Fusion Energy Sciences within the Office of Science, and that program is slated for sharp cuts in the president's 2013 budget. While the science office also funds some inertial fusion research, research on other techniques is supported by the department's National Nuclear Security Administration because inertial fusion can also be used to simulate nuclear explosions. In addition, Congress has ordered DOE to carry out a program looking into high repetition rate lasers.

Most fusion research focuses on magnetic confinement, using powerful electromagnets to contain a thin plasma of hydrogen isotopes and heat it until the nuclei fuse. Inertial confinement is an alternative method in which small capsules of hydrogen-isotope fuel are crushed to produce the intense temperature and pressure needed for fusion to occur. Although researchers have been working on inertial confinement fusion for more than 50 years, no device has yet achieved ignition. NIF, which was completed in 2009, is aiming achieve ignition by the end of September, to but progress has been slower than expected.

The committee's interim report concludes that "many of the technologies needed … are still at an early stage of technological maturity." Those technologies include the "driver" used to crush the fuel capsule, such as lasers, heavy ion beams, or powerful pulses of electric current. The driver can also be trained either directly onto the fuel capsule or indirectly onto a heavy metal container, which then heats the capsule inside by bathing it in x-rays. Other issues for a power reactor will be developing a reaction chamber that can withstand intense neutron bombardment for years on end and discovering a way to produce the fuel capsules quickly and cheaply (a reactor may consume a million or more capsules every day).

The report also notes that while "there have been impressive R&D efforts to develop a wide range of driver technologies … very little effort has been spent on developing the technology of the reactor chambers or on addressing materials problems peculiar to inertial fusion."

A study by NIF on a future inertial fusion facility resulted in a conceptual design dubbed the Laser Inertial Fusion Energy (LIFE) plant. Such a demonstration plant could be built in 12 years if researchers employ components that are commercially available and use NIF technology. But some researchers are skeptical of that claim. "The extreme optimism of some advocates of LIFE is unsupportable," says Robert McCrory, director of the Laboratory for Laser Energetics at the University of Rochester in New York state, who is not a member of the NRC committee.

Instead of backing the frontrunner, the NRC committee has come down on the side of a diverse program of research. "There's a fairly long and challenging technical road ahead for all these techniques, including LIFE," says Ron Davidson of Princeton Plasma Physics Laboratory, co-chair of the committee. The interim report concludes that, "based on the presentations and materials provided, ... it would be premature to down-select among driver options at the present time."

The committee's final report is due out at mid-year, and its impact will likely be shaped by NIF's performance this year. "Until we see some evidence that fusion is going to work, it would be premature to invest large amounts in technology," McCrory says.

Posted in Physics, Policy