It's late April and workers are assembling the last parts of the National Ignition Facility (NIF), a sprawling building covering the area of three football fields at Lawrence Livermore National Laboratory in Livermore, CA. Dressed in hard hats, hair nets, lab coats, and latex gloves, they have gathered at the target chamber, a sphere 10 meters in diameter and bristling with 48 burnished-aluminum ducts that together house 192 separate laser beams. Each beam on its own is one of the world's most powerful, says Bruno Van Wonterghem, operations manager at NIF. Together they deliver 50 to 60 times the energy of any other laser.

The workers are preparing to install a key piece of equipment--the target-alignment sensor--at the end of a tapered boom that can be extended into the center of the chamber. Scientists will use the sensor to position a gold canister the size of a pencil eraser at the center of the sphere and align it with the laser beams. In a series of experiments over the coming months, if all goes according to plan, those lasers will strike the gold canister with a pulse 3 to 20 nanoseconds long, generating a bath of high-energy x-rays. These in turn will cause a two-­millimeter pellet containing hydrogen isotopes to implode. "All of that kinetic energy gets transformed into heat," says Van ­Wonterghem. The hydrogen pellet will reach a temperature of 100 million °C and a density 100 times that of lead--enough to start a fusion reaction.