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Comment by Animats | Hacker News Reader

Oh, this is just laser fusion. One pulse of power. That's not a power source, even potentially. It's a lab-sized H-bomb experiment. This isn't one of the magnetic containment systems achieving ignition and sustaining the reaction. Now that would be an achievement.

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Internal combustion piston engines also do intermittent combustion. If you were to make a power plant based off of this, you would need dozens of these per second (and much more efficient lasers and a tritium breeding liquid lithium metal jacket and… a lot of other stuff).

The capsules are tiny and do not generate usefull amount of energy.

ITER is planned to generate 500,000,000W. Thats actually usefull

500MW of heat from 620MW of electricity seems far from useful. Interesting, but not useful.

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.

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.

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.

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

According to Sabine Hossenfelder, ITER will only actually generate 0.57 of what's put in. The large number out isn't the full story.

http://backreaction.blogspot.com/2021/10/how-close-is-nuclea...

> You have seen in the earlier quotes about ITER that the energy input is normally said to be 50 MegaWatts. But according to the head of the Electrical Engineering Division of the ITER Project, Ivone Benfatto, ITER will consume about 440 MegaWatts while it produces fusion power. That gives us an estimate for the total energy that goes in.

> Though that is misleading already because 120 of those 440 MegaWatts are consumed whether or not there’s any plasma in the reactor, so using this number assumes the thing would be running permanently. But okay, let’s leave this aside.

> The plan is that ITER will generate 500 MegaWatts of fusion power in heat. If we assume a 50% efficiency for converting this heat into electricity, ITER will produce about 250 MegaWatts of electric power.

> That gives us a Q total of about 0.57. That’s less than a tenth of the normally stated Q plasma of 10. Even optimistically, ITER will still consume roughly twice the power it generates. What’s with the earlier claim of a Q of 0.67 for the JET experiment? Same thing.

The roadmap has always been: ITER, DEMO [1] and then PROTO [2].

"DEMO refers to a proposed class of nuclear fusion experimental reactors that are intended to demonstrate the net production of electric power from nuclear fusion." [1]

So indeed the road is long, and ITER is not DEMO, and DEMO is not PROTO. I've read a lot of good arguments against ITER, but ITER not being DEMO is not one of them.

By the way, just to be pedantic: ITER will not actually generate 0.57 of what's put in. It would only generate 0.57 of what's put in, if someone bothered to hook a generator to it. But since no generator will be hooked, it will generate exactly 0 Watts of electricity. Generated heat will simply be dissipated away. To be net positive in production of electricity, EU DEMO is expected to have a Q of 25...

[1] https://en.wikipedia.org/wiki/DEMOnstration_Power_Plant

[2] https://en.wikipedia.org/wiki/PROTO_(fusion_reactor)

Well...yeah. The national labs do fusion experiments because they can't do bomb tests any more. (It's also the reason they tend to have the biggest supercomputers in the world, so they can simulate nuclear explosions.) But that doesn't mean they don't learn things that might be useful for energy production.

The test ban treaty was a slick example of pulling up the ladder after arriving somewhere first. Want weapons research? Now you need weapons researchers and supercomputers...

The laser produced 1.3 MJ from fusion in an instant using only around 250 KJ of laser energy. We have already created machines that fuse hydrogen and from only 3 KJ of electricity, produce 10^10 MJs of energy out of it in an instant.

I never got the appeal of the laser experiments, they must be covers for weapon research.

It's not a cover, it's an explicit purpose of the facility:

NIF uses lasers to heat and compress a small amount of hydrogen fuel with the goal of inducing nuclear fusion reactions. NIF's mission is to achieve fusion ignition with high energy gain, and to support nuclear weapon maintenance and design by studying the behavior of matter under the conditions found within nuclear weapons

Like many other advancements, civilian use has been a nice side effect of the primary driver of advancement.

Cheaper lasers that are useful for diagnostics in actual fusion energy research machines?

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