The NIF, which is more than 80% complete, is a 10-story building in which 192 laser beams focus on a tiny target inside a 30-ft-diameter aluminumlined chamber. So far, eight beams have been commissioned.
When fully operational (scheduled for mid-2009), NIF will be used to study and achieve ignition, the production of a brief burst of energy greater than that used in its creation. Ignition, or nuclear fusion, has never happened under controlled conditions in a laboratory setting.
NIF's first four beams were fired into various-sized goldplated cylinders (hohlraums) only a few millimeters long. The laser beams enter through a single hole at one end of the hohlraum. In future NIF ignition experiments, the deuteriumtritium fuel capsule will reside in a larger hohlraum. All 192 beams will then heat the interior of the hohlraum through holes on both ends, creating X-rays that burn off and implode the capsule to ignition.
The high-power UV laser beams last 9 nsec at most — a long time by ignition standards. Such sustained pulses are unique to NIF.
Various diagnostic instruments measure the X-ray spectra and radiation temperatures inside the hohlraum and image X-rays that are energetic enough to exit through the hohlraum wall. Snapshots of the X-rays provide a clear picture of how the plasma evolves inside the hohlraum.
The NIF findings are important because they confirm that larger hohlraums should develop plasma more slowly, an important factor in controlling proper symmetry of the implosion necessary for ignition.