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Comment by smaddox | Hacker News Reader

1 MJ is enough to vaporize roughly half a liter of water that started at room temperature. That's nothing to sneaze at. Obviously you would need to do with a high rate (e.g. once per second) in order for it to be viable for power production. No reason the lasers couldn't do that. The challenge is making the pellets cost effective at scale. Currently, they cost something like $10k each.

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1 MJ per second is 1 MW, a power level typical of portable diesel generators. Conventional nuclear plants are hundreds of megawatts each.

Apparently it is quite hard to repeat the laser blast quickly, because the optical system heats up during a pulse causing the beams to deflect as the materials expand and contract due to temperature. The NIF design requires dozens of laser beams to align precisely on a very small pellet in the middle of a large cavity. If you fire it a second time before it completely cools down the beams will hit the pellet slightly off-center and you won't get the compression needed for efficient fusion.

Portable as in a trailer, right? 1MW is around 1340 horsepower.

The bigger problem is the precision-machined hohlraum the pellets sit in for ignition. That costs millions of dollars, is crucial for actually achieving anything, and is destroyed in the process.

I wondered why these things were so expensive until I read:

-literally made of gold or uranium

-walls must have surface roughness less than 1 micron

Are there other reasons too? I'm not sure where to find machinable uranium on McMaster

Uranium is pretty cheap, they don't need enriched uranium (although I'd be interested to know if using the fusion as a neutron source could trigger a decent amount of fission in the hohlraum), they just need a very dense metal.

You should take a look at the LLNL's page on targets.

https://lasers.llnl.gov/about/keys-to-success/targets

https://www.lanl.gov/conferences/tfm/presentations/08-21-12-...

I think the marginal Hohlrahm shot cost may be lower, like $10,000 or something, but that’s way too high for just 1MJ (.3kWh thermal, roughly… 0.1 kWh worth of electricity). They need to figure out a mass production method (to get shot cost to pennies) plus they need to increase the yield per shot by at least an order of magnitude.

It’d have to be dozens or even hundreds per second, like an internal combustion piston engine.

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