Earlier this year, there was much rejoicing in the halls of the Lawrence Livermore National Laboratory (LLNL--Livermore, CA) with the welcome news that the 1998 federal budget would contain funds to start the National Ignition Facility (NIF), a giant project that is conservatively estimated to cost a whopping $1.2 billion. That was also good news for a number of suppliers of optical components for the 192 lasers that will make up the massive NIF. But is the NIF a strategically necessary project or just another "big science" toy to keep LLNL`s talented physicists in work? It is by no means clear that Lawrence Livermore should have been given the green light to begin the ground-breaking for the NIF. It is not too late to switch off this project. The NIF has come into play as a key part of the US Department of Energy`s nuclear weapons stockpile stewardship program, in itself an estimated $40 billion effort. With the cessation of the Cold War and the subsequent moratorium on underground nuclear testing, the DoE says it needs to be sure that the US national stockpile of nuclear weapons is kept in good shape. The weapons guardians can`t very easily go poking around in the bombs to see how they are aging, and the moratorium prevents testing actual samples. This means that scientists at Los Alamos National Laboratory (Los Alamos, NM) have to rely on computer simulations to tell them how the venerable bombs would perform should they ever be needed again. But the simulations are in need of experimental validation, claim the scientists.
Nuclear fusion in miniature
Thus the NIF is an attempt to model thermonuclear fusion in microcosm with a technique called inertial confinement fusion (ICF). The theory of ICF is that the NIF`s giant lasers will produce megajoule pulses of ultraviolet light focused to explode a tiny gold capsule, called a hohlraum, that contains a frozen pellet of deuterium and tritium. Just before the hohlraum explodes, it is expected to emit a powerful blast of x-rays that will compress the pellet and heat it to more than 100 million degrees Celsius. If successful, the deuterium and tritium nuclei will fuse as in a nuclear bomb but on a very much smaller scale. If all this sounds very difficult, it is. No-one knows if the NIF stands much chance of success.
Several leading physicists have estimated the NIF`s chances of success as being less than 10%. Even the most ardent supporters of the NIF are hard pressed to give it a better than 50-50 chance of obtaining nuclear fusion. For a start, experts question whether the laser optics will be able to stand up to the energies required to come close to fusion. If damage concerns are not met, light intensities will have to be reduced, which will probably mean that fusion will not be reached. Other experts question whether the targets can be made with sufficient surface smoothness to ensure that the pellets will be evenly heated. There are also several questions about the stability of the hohlraum itself.
However, even if fusion does not occur, NIF supporters argue, the project will attract and keep highly talented physicists, much useful data will be generated, and Congress will be persuaded to continue the moratorium on underground nuclear testing. As a scientist, I`m happy to see good physicists usefully employed but if, as seems likely, the Comprehensive Test Ban Treaty is ratified by Congress, why should taxpayers continue to foot most of LLNL`s wage bill? As to the question of generating useful data, I`ve yet to see what an untested NIF is expected to produce that could not be generated by continuing the much smaller--and far less expensive--Nova project currently under way at LLNL.
A skeptical Congress
Fortunately, the House and Senate committees that oversee DoE appropriations also appear to be skeptical about the projects that make up the nuclear stockpile stewardship plan. It seems likely that Congress will not approve NIF funding beyond FY1998, which means that the program will be scrutinized carefully in committees. Let`s hope that the committee members are not blinded by flashes of light representing the unrealistic promises of laser-generated thermonuclear fusion.