The National Ignition Facility, a half-billion-dollar bid [$3.5billion to build, total program estimated to be over $5billion]
to ignite a fusion "burn," is drawing a surprising following, aided by favorable reviews of the existing laser fusion program Only a test
Still, physicists familiar with the program caution that it should not be oversold. For one thing, if and when NIF gets built- which could happen by 2001-laser fusion will still have a long way to go to become a practical energy source. The best NIF can offer, says Marshall Rosenbluth, a University of California, San Diego, physicist and a member of the ICFAC panel, is "a proof of principle test of inertial fusion either for defense applications, or in the longer run for energy applications."
That's because NIF, like Nova, would be what the physicists call a one-shot target experiment. "The laser could fire perhaps once an hour," says Lindl, because "a lot of waste heat comes off, and you have to allow the optics to cool." A fusion power plant would have to achieve the same implosion feats as NIF-but at the rate of at least five to ten times a second. The best bet for drivers that could achieve such repetition rates are heavy ion accelerators, says [Mike] Campbell [then head of NIF],
and Livermore is working in collaboration with the Lawrence Berkeley Laboratory to develop them. Like lasers, the ion beams would bombard a hohlraum, which would emit x-rays and compress the pellet. But because they focus their beams using magnetic fields, accelerators are more resistant to neutrons and heat, and they're also far more efficient than glass lasers.
Such devices are at least a few decades in the future, however. For now, says Lindl, lasers are the best tool for studying ICF: "A lot of what we learn about hohlraums and pellets [at laser facilities] carries over to ion beams." And, for now, lasers also provide the best shot for achieving ignition. "When laser fusion started up," says Massachusetts Institute of Technology physicist Arthur Kerman, an ICFAC panelist, the technology "was eight orders of magnitude, 100 million times away, from a sensible version of what was needed. They have come a very long way in 30 years. They may have come far enough."
page 1506 SCIENCE * VOL. 262 * 3 DECEMBER 1993