At the National Ignition Facility: Two million joules of ultraviolet laser energy converges on a cylindrical target called a hohlraum (shown above), which houses a tiny pellet of deuterium and tritium. Image: j-fi/Flickr
LIVERMORE, Calif. -- In the dark early morning hours, scientists conduct an almost daily ritual out here at the National Ignition Facility at Lawrence Livermore National Laboratory: a countdown. In a NASA-style control room, researchers and technicians huddle around LCD monitors on semicircular desks facing a wall of five projection screens.
The countdown reaches zero, the world's most powerful laser fires silently for a fraction of a second at a fuel target, and results pour in. The equipment winds down, and scientists spend the next day poring over numbers, checking instruments and preparing for the next shot.
"In some ways, it's the most disappointing end of a countdown because you don't see something blasting off into the sky," said Mike Dunne, director of laser fusion energy at NIF. "You wait a few hours to get the data, and then it becomes exciting again."
Though it is a bit anticlimactic compared to a rocket launch, scientists here are nevertheless aiming for the stars with every attempt at ignition.
Specifically, they want to harness fusion, the reaction that fuels the sun and other stars. Outside the main entrance of the facility, a building resembling a warehouse spanning more than three football fields, a banner cheerfully exclaims, "Bringing Star Power to Earth."
Our sun turns 600 million tons of hydrogen into helium every second, creating the heat and light that bathe our planet 93 million miles away, driving air currents, feeding plants and tanning skin. Bottling and channeling even a minuscule fraction of that energy here on Earth would radically change the world's economy and humanity's footprint on the environment.
"It just suffers from the one small problem that nobody's ever shown it to work," Dunne explained.
The long road to ignition
While the hydrogen bomb program proved man could liberate fusion energy, harnessing it for peaceful purposes has been a struggle since the 1940s. Researchers have overcome challenges only to see new ones present themselves. Now, with tight funds, waning public patience and an increasingly urgent need for solutions to climate change, fusion research faces uncomfortable questions of which direction to go, how to get there and what gets left behind.
In the United States, government-funded labs are simultaneously pushing two tracks -- inertial fusion and magnetic confinement fusion -- but neither with the vigor needed to advance the field meaningfully, according to scientists. Though researchers on both sides tout their accelerating progress, neither has achieved ignition, the threshold where the reaction gives off more energy than is needed to start it.
Think of a campfire. A lone spark might not be enough to start a roaring flame, but lighting some tinder could bring the logs alight. At this stage, scientists are still using too much tinder and not burning enough of the wood to make a campfire worthwhile.
However, for the most part, they understand the physics behind fusion. In particular, researchers want to fuse two hydrogen isotopes. The hydrogen we know and love, also called protium, is simply one proton encircled with one electron. Stick a neutron onto that proton and you have deuterium, which is naturally present in seawater in concentrations of roughly one part per 6,000. Add two neutrons and you have tritium, which is rare since it has a half-life of only 12.3 years.
In a fusion reaction, you want to get one deuterium to stick to one tritium, forming a helium nucleus of two protons and two neutrons. In the process, the reaction kicks off the extra neutron, which can fly off to boil water or another heat transfer fluid.
It also turns out that the newly formed helium nucleus is less massive than the sum of its parts. The difference in mass dissipates as energy governed by Einstein's famous formula, E=mc², where the energy equals the mass times the square of the speed of light. This means a very tiny amount of stuff can yield a huge amount of energy to propagate the fusion reaction.