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

Science

[Anonymous Coward]

Personally I think they'd have an easier time of it if they combined different ideas, but what do I know?

I don't think that the goal is simply to generate lots of electricity, but rather to setup and run an experiment that could teach them new things. (Oh, and generate oodles of research papers.)

Usually, in these kinds of basic "understanding" tests (which is still where we really are in terms of our understanding of quantum effects), you don't want to combine multiple strategies ...

Really Firing Up?

[4of12]

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.

Have any hard promises or milestones been met about Tera-Watt-seconds/mm^3 that the hohlraum will experience?

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

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

Re:Fluid dynamic instabilities, too

[Iainuki]

NIL isn't a facility for researching fusion power: it's designed for nuclear weapons research, even though no one says that in public (it's said more often in private).

The enormous technical difficulties involved in getting fusion from this method, much less positive energy returns, is one pointer to this fact; compare it to magnetic confinement, which has produced fusion though not positive energy returns. However, nuclear weapons researchers have spent years looking for more controlled circumstances under which to study how fusion occurs in bombs. After the US signed the CTBT, this need became more urgent, thus we're seeing it get built.

meanwhile, the big fusion reactor

[iggymanz]

in the sky continues to burn 24x7 at no cost, most of its energy completely unused

Re:meanwhile, the big fusion reactor

[Beryllium Sphere(tm)]

>in the sky continues to burn 24x7 at no cost, most of its energy completely unused

Yeah, but look how many cases of cancer it's causing. It can't be stored safely because it will remain radioactive for billions of years. There is no realistic plan for decomissioning. Some research implicates it in global warming and it's known to cause destructive storms. Concentrated exposure has been shown to cause smoking and charring in ants.

Other reactors of the gas-core gravitationally confined design have been known to explode, causing great environmental damage.

As soon as someone gets around to filing and reviewing an Environmental Impact Statement, we'll have to shut down that huge nuclear reactor in the sky and replace it with alternatives that environmentalists can accept.

Solar fusion reactor

[Latent Heat]

While the Sun is cranking out energy from fusion, it is notworthy how low the reaction rate. Now it is burning H into He using the proton-proton reaction (hotter stars use the carbon cycle), not a reaction that is practical for any Earth-based fusion reactor, the temperatures and pressures at the core are enormous, but the reaction rates are rather low.

Think about it -- the Sun has an estimated 10 billion year Main Sequence lifetime, of which it has used up 5 billion years. Also consider that over the Main Sequence lifetime it cannot achieve anywhere near complete burnup of the hydrogen and you can figure that the amount of hydrogen burnt per year is measured in parts per trillion.

There are heavier stars that burn their hydrogen much more quickly, and it is good for us that the Sun is so thrifty, but if you could duplicate the conditions in the core of the Sun, it wouldn't make for an economical energy source in an Earth-based power plant.