The US National Ignition Facility will focus on nuclear fusion research. Credit: LLNS/LLNL/US DEPT OF ENERGY

The US National Ignition Facility (NIF) in Livermore, California, is almost ready to fire up its 192 laser beams to recreate the Sun's fusion burn.

The last of the project's 6,206 optics units — the mostly glass and crystal components that focus the lasers onto a tiny target — was installed on 26 January. It marked the end of the US$3.5-billion facility's construction ahead of a federal deadline of 31 March.

After years of delay and hundreds of millions of dollars in overrun costs, "the project is, for all intents and purposes, completed", says NIF director Edward Moses. He will now focus on ramping up the 'shots' of laser light. On hitting the target, the shots create temperatures of more than 100 million degrees and pressures that are thousands of times greater than at Earth's core, which scientists hope will trigger nuclear fusion. Although smaller lasers have achieved petawatt (1015 W) powers in femtosecond (10−15 s) bursts, NIF's total energy will exceed that of any current facility. Its goal is to reach 1.8 million joules, far greater than the 40,000 joules generated by the current leader: OMEGA at the University of Rochester, New York. It is likely to remain at the top until a similar facility, the Laser Mégajoule near Bordeaux, France, is completed in 2010.

Experiments have already begun towards NIF's primary mission: finding other ways to certify the safety and reliability of decades-old thermonuclear weapons rather than testing them underground. However, some critics have questioned whether this research will contribute much towards 'stockpile stewardship' (see _Nature_ 407, 129–130; 2000).

Still, there are other reasons for NIF. This year, scientists will use the machine to explore astrophysical questions, such as how the implosion of a massive, dying star leads to supernova explosions. And Raymond Jeanloz, a geophysicist at the University of California at Berkeley, wants to probe the conditions expected inside giant exoplanets: "There's a regime at these high pressures where the chemistry is wonderfully and totally different," he says, "and it has never been accessed experimentally."

As NIF's shots reach full strength, perhaps as early as 2010, a third community will be feeling excited: those who hope to use nuclear fusion as a potential source of energy. A competing technique, used by fusion projects such as ITER in Cadarache, France, traps hydrogen fuel in magnetic fields while heating it to temperatures far greater than that of the Sun. Although both laser- and magnetic-fusion machines have achieved bursts of energy from fusion, none has achieved the conditions necessary for self-sustained fusion power. NIF's proponents think they have a chance. "We've been waiting for this since the 1960s," says Moses.