— Is nuclear fusion the ultimate energy source, or the ultimate pipe dream? Millions upon millions of dollars are being spent to find out which answer is the right one. For some technologies, the answer could come sooner than later. For others, it may be later rather than sooner.
The easiest way to access fusion power is to go outside on a sunny day: Nuclear fusion is the reaction that powers the sun, by crushing hydrogen atoms into helium atoms and converting the small blips of extra mass into energy. Hydrogen bombs, tested by the world's armies but never used on the battlefield, do the same thing.
For decades, scientists have been trying to figure out how to harness the fusion reaction to generate electrical power. A key milestone would be passing the "break-even" point, at which a controlled fusion reaction produces more energy than it consumes. Research aiming toward that goal is moving along three main routes, and the pace of progress can vary, depending on which road you're traveling down. Here's a status report on the fusion race:
Laser fusion: On the rise
The biggest buzz is being generated at the National Ignition Facility, the $3.5 billion laser research site at California's Lawrence Livermore National Laboratory. NIF is designed to produce fusion power on a small scale by aiming 192 laser beams simultaneously at a hydrogen target the size of a pencil eraser for a burst lasting just a few billionths of a second.
In the shorter term, the experiment will help the U.S. military simulate how thermonuclear warheads work so that the strategic arsenal can be kept up to date. In the longer term, the laser-blaster could point the way toward commercial power-generating schemes.
NIF was certified for operation in March, and last month officials reported that the laser beams could generate enough X-ray energy during the initial testing phase to ignite the fuel capsules as required. The research campaign is scheduled to begin in earnest early next year, and there's already talk in the fusion community that the reaction could reach the break-even point by the time 2010 ends.
Then what? Such an achievement could clear the way for laser facilities designed for more extended operations, such as the instruments pioneered by the Livermore Lab's Mercury laser project. NIF researchers are also looking at a plan to use neutrons from a fusion reaction to boost the efficiency of a nuclear fission reactor — a hybrid concept known as Laser Inertial Fusion-Fission Energy, or LIFE.
Inertial electrostatic fusion: Moving quietly
The dark horse in the fusion race is an approach known as inertial electrostatic confinement fusion, or Polywell fusion. This method, pioneered by the late physicist Robert Bussard, involves designing a high-voltage cage in such a way that atomic nuclei slam into each other at high speeds, sparking fusion.
Bussard claimed that Polywell fusion could lead to low-cost commercial fusion power and usher in a new generation of space propulsion systems as well. After his death in October 2007, his work was carried on by a small team of physicists operating out of Bussard's EMC2 Fusion lab in Santa Fe, N.M.
In September, EMC2 Fusion was awarded a Navy contract, backed by $7.9 million in stimulus funds, to develop a scaled-up version of a Polywell fusion reactor. Development and testing of the device is expected to take two years, and there's an option to spend another $4.4 million on experiments with hydrogen-boron fuel (known as pB11).
In the past, EMC2 Fusion's Richard Nebel has been able to describe the team's progress in general terms, saying that he was "very pleased" with the performance of an earlier test device. But now, with more Navy money on the line, Nebel has been constrained from saying anything about the project. The fact that the research is continuing, however, appears to indicate that the results have been promising enough to keep the Navy interested.
Private-sector ventures are pursuing a range of similarly unorthodox approaches to small-scale fusion — but it's not yet clear how big the payoff might be. Among the ventures that have surfaced so far are Lawrenceville Plasma Physics, Tri Alpha Energy and Helion Energy.
Magnetic fusion: Not so fast
When it comes to fusion research, the road most traveled is the one that features magnetic containment of fusion plasma, usually within a doughnut-shaped chamber known as a tokamak. The current poster child for magnetic confinement fusion is the ITER project, headquartered in southern France.
ITER, which started out as an acronym standing for "International Thermonuclear Experimental Reactor," is projected to spend $13 billion over 30 years to demonstrate a break-even fusion reaction in an eight-story-high containment vessel. Components for the device are to be contributed by the ITER consortium's seven parties — the European Union, China, India, Japan, Russia, South Korea and the United States.
The facility is just in the beginning stages of construction, and the current schedule calls for the reactor to start up in 2018. However, Science magazine reported last week that the project's governing council held back its endorsement of the schedule, saying that the proposed startup date did not seem realistic.
"Europe is very concerned about the risk of pushing ahead too fast," Steven Cowley, head of Britain's Culham Center for Fusion Energy, told Science.
So what would happen to the ITER project if it turns out that other, cheaper routes to the break-even point bear fruit on a shorter timetable? That sounds like something worth talking about ...