National Ignition Facility is Firing Up

VernonNemitz writes "Over near San Francisco in California, USA, the Lawrence Livermore National Laboratory is starting to reach the end of 15 years of development work on the National Ignition Facility. The goal is to use 192 high-powered laser beams to blast a pellet of frozen hydrogen isotopes, turning it into a tiny (and thus safe) hydrogen bomb. Currently 4 of the lasers have been commissioned for use in tests; the eventual goal is to get more energy out of the exploding pellet than is dumped into it. Personally I think they'd have an easier time of it if they combined different ideas, but what do I know?"

Comments

Fluid dynamic instabilities, too

[GuyMannDude]

From what little I understood, it was an extremely challenging, perhaps even overly ambitious effort to get all 192 lasers to be sufficiently well-focussed in a perfect sphere and with perfect timing, perfect power levels etc.

It's more than just that. These lasers are used to irridate the outer hell of a spherical metal shell surrounding layers of "stuff" and, ultimately, a deuterium-tritium pellet at the very center. The lasers vaporize the outer hull of the metal tamper, causing near-instantaneous stresses in the remaining metal. This causes a spherical shockwave to form and begin to implode. As it passes through the inner layers of the target, microscopic manufacturing imperfections in the spherical layers (you can never create a perfectly sphere layer) lead to instabilities in the shock wave as it passes from material to material. Fluid dynamic instabilities such as Richtmyer-Meshkov and Raleigh-Taylor causes the spherical symmetry of the shockwave and the layers to break down. Gross mixing of the layers occurs and the shockwave doesn't implode to a nice point like one would hope. Therefore, no fusion of the deuterium and tritium.

Little is known about how to control these instabilties. So even if you got all the lasers to work correctly to form a perfect shockwave, the travel of this wave through the imperfectly-created layers ultimately causes the reaction to break down anyhow.

It's a very hard problem. I would guess it would take even more time and money than it has already.

You said it. Some would argue that because of the above listed problems that magnetically-confined fusion is the way to go. But that approach has its own set of problems.

GMD

Tiny, safe bomb is accurate.

[guybarr]

Besides, the reaction that occurs in the fusion chamber of the power center is not a bomb, it is controlled fusion, much more elegant (and more expensive).

In ICF the goal is a submilimeter scale thermonuclear explosion. A tiny bomb is indeed an accurate description.

It is indeed safe b/c the quantities are small: nuclear energy density is ~10^6 higher than chemical, so if one explodes 10^-6 the amount of, say, coal that is burned in a usual generator in a second, one gets the same power, which we know how to control (puting aside the nutronic difficulty).