The "Grand Central Station" of the National Ignition Facility is the target bay, which houses the final optics assemblies, diagnostics, and the target chamber.
Pulses from NIF's 192 high-powered lasers, in a journey that originates more than 100 meters away in the master oscillator room, race towards the target bay with incredible precision. When they arrive at the center of the target chamber, they deposit up to 500 trillion watts of power for 20 billionths of a second on an eraser-sized capsule containing a target the size of a BB. Surrounding the target are numerous diagnostics that examine in minute detail the arrival of the laser beams and the reaction of the target to this sudden deposition of energy. Temperatures of 100 million degrees and pressures extreme enough to compress the target to densities up to 100 times the density of lead are created.
The target bay is a concrete silo 30 meters high and 30 meters in diameter. The target bay is filled with laser, diagnostic, and other utility/support equipment needed to conduct experiments safely and reliably.
The target chamber and utility systems provide the vacuum environment needed during the experiment, hold the final optics assemblies that focus the laser light on the target and contain debris and X-rays generated during experiments. The chamber, a sphere 10 meters in diameter, was assembled from ten-centimeter-thick aluminum panels that were pre-formed and then welded in place. It is covered with 0.3 meters of concrete that has been injected with boron to absorb neutrons from fusion reactions. The target chamber is filled with holes that permit the laser beams to enter the chamber and to provide viewing ports for all of the diagnostics.
Laser beams enter in groups of four called quads; two quads make up a bundle, and six bundles constitute a cluster. Four clusters—two in each of the two laser bays—add up to NIF's total of 192 laser beams. Diagnostic ports are about one-half meter in diameter and are generally concentrated around the "waist" of the target chamber
Target handling systems precisely position the target at target chamber center and freeze the target to cryogenic temperatures so that the fusion reactions can be more easily achieved. Seven-meter-long positioners are located just outside the target chamber. They can be retracted to permit installation of a target and then extended to its position at target chamber center. Most targets are maintained at very cold temperatures, about -250 degrees centigrade (see Cryogenic Target System). One of the positioners can maintain this temperature precisely to a tolerance of better than 0.001 degrees centigrade.