Sun in a Bottle - Charles Seife [101]
It was as if everything that could possibly go wrong with NIF was, in fact, going wrong. Some of the issues were minor annoyances: a brief delay in construction followed when workers found mammoth bones on the NIF site. Some were major: the glass supplier was having difficulty producing glass pure enough to use in the laser, forcing a revamp of the entire manufacturing process. Some were just bizarre. The head of NIF, Michael Campbell, was forced to resign in 1997 when officials discovered he had lied about earning a PhD from Princeton University.
Some problems were unexpected but easy to deal with, such as an issue with the capacitors, the devices that store the energy used to pump the laser glass. These devices were packed so full of energy that occasionally one would spontaneously vaporize. It would explode, spraying shrapnel around the room. Engineers solved the problem by putting a steel shield around the capacitors; when one exploded, flapper doors would open and the debris would spray toward the floor.
Some problems were more complex. For example, scientists had long since gone from infrared to green to ultraviolet light to reduce the disproportional heating of electrons compared with nuclei, but ultraviolet light at such high intensities was extremely nasty to optics. It would pit anything it came into contact with. The laser would damage itself every time it would fire. The solution was less than perfect: at NIF’s full power, the optics will have to be replaced every fifty to one hundred shots or so, an extremely expensive prospect.
Furthermore, scientists were still struggling to deal with the Rayleigh-Taylor instability—the one that turns small imperfections on the surface of the fuel pellet into large mountains and deep valleys, destroying any hope of compressing the fuel to the point of ignition. Not only did scientists have to zap the target very carefully—so that the energy shining on the target was the same intensity on every part of the pellet—they also had to ensure that the pellet was extremely smooth. Even tiny imperfections on its surface would quickly grow and disrupt the collapsing plasma. To have any hope of achieving ignition, NIF’s target pellets—about a millimeter in size—cannot have bumps bigger than fifty nanometers high. It’s a tough task to manufacture such an object and fill it with fuel. Plastics, such as polystyrene, are relatively easy to produce with the required smoothness, but they don’t implode very well when struck with light. Beryllium metal implodes nicely, but it’s hard to make a metal sphere with the required smoothness. It was a really difficult problem that wasn’t getting any easier as NIF scientists worked on it.
The cost of the star-crossed project ballooned from about $1 billion to more than $4 billion; the completion date slipped from 2003 to 2008. Worst of all, even if everything worked perfectly, even if NIF’s lasers delivered the right power on target, nobody knew whether the pellet would ignite and burn. As early as the mid-1990s, outside reviewers, such as the JASON panel of scientists, warned that it was quite unlikely that NIF would achieve breakeven as easily as advertised. The prospects for breakeven grew worse as time passed. By 2000, NIF officials, if pressed, might say that the laser had a fifty-fifty shot of achieving ignition. NIF critics, on the other hand, were much less kind. “From my point of view, the chance that [NIF] reaches ignition is zero,” said Leo Mascheroni, one of NIF’s main detractors. “Not 1%. Those who say 5% are just being generous to be polite.” The truth is probably somewhere in between, but nobody will know for sure until NIF starts doing full-scale experiments with all 192 beams.
If NIF fails to ignite its pellets, and if it fails to reach breakeven, laser fusion experiments