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Comment by walnutclosefarm | Hacker News Reader

Actually, I think the pedanticism is on the part of the people announcing this "breakthrough." The definition of "break even" used here (that is, Q>1) is highly technical, and but one factor in the actual "break even" equation. This experiment didn't prove you could get more energy out of a fusion burn than you put in (which is the notion they want to evoke), but rather that they could raise the ratio of energy absorbed in one part of the burn, from the NIF lasers, to that released in another, from 0.7, which they had achieved in August of 2021, to 1.5. That's it. That, and the fact that it's funding season in Washington, so not a bad time blow NIF's horn.

Milestone, yes. You have to get Q above one if you're starting at .01, and need to get to 100 and 1 is a great mile marker. But, But breakhrough - I don't think so.

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I mean NIF has spent a majority of its life (11 years) seeing yields below 200 kj. Only in 2021 did it jump above 1 mj and in 2022 above 3 mj. If your definition of breakthrough is rapid improvement, I think this demonstrates it:

See below for previous yields of NIF shots. https://en.wikipedia.org/wiki/National_Ignition_Facility#/me...

I realize this may be too complicated to explain in one comment, but as a layperson... can anyone summarize what they actually did to achieve this sudden gain in power? Like, what have they been doing for those 11 years? Upgrading the lasers, improving the optics, refining the design of the hohlraum, changing up the fuel? I know this is the cutting edge of physics and all, and maybe there's some DoE secrecy involved, but it's interesting that I haven't seen a single article yet attempt to summarize what changes were actually made in order to achieve the "breakthrough".

I don't think anyone specifically knows. If you ask the physics, they will point to changes (like pulse shape or component sizes) they made due to their increased understanding of the physics. If you ask the target design people, they will point to decrease fill-tube size and number of defects in the capsule. If you ask the facility, they will say their ability increase both power and control power delivery. Likely, it is a combination of everything.

The other point that has been mentioned to me is when you in the self heating regime, there are exponential returns on increasing "quality" of a shot.

Thank you!

What does "component sizes" and "fill-tube size" refer to, BTW? And the quality of a shot thing you mention in the last line? Sorry for all the questions, just curious

This powerpoint from last February has a good rundown in the context of the 1.35GJ shot from August 2021:

https://www.orau.gov/support_files/2022ssap/presentations/Da...

>The definition of "break even" used here (that is, Q>1) is highly technical, and but one factor in the actual "break even" equation.

Isn't the Qplasma > 1 the most important one here, by a very wide margin? Maybe the only important one at this point in time. That fusion begets more fusion, in a positive-feedback way. That's the breakthrough here. All the other efficiency factors are secondary in nature. That is step 1, and the next step is to scale this up so that eventually Qplasma >> 1. And only then the hand wringing about efficiency of the lasers becomes something to address. It seems like the baby was just born, and people are concerned about which colleges to apply to.

NIF achieved plasma combustion over a year ago, as documented in a Nature article earlier this year. If there is a threshold being crossed, that was it. The recent shot tuned that experiment to increase the yield. So now the the total released energy (not capturable, or usable, but released) is greater than the total non-fusion energy captured by the target (not put on the target, but actually captured and turned into useful heating and compression). But that's a completely arbitrary milestone.

And, most significantly to me, there is no argument being made anywhere that this milestone is on the path to anything other than a dead end, local optima. That is, that you can further optimized the shape, quality and size of the hohlraum, and shape of the laser pulse to get to a Q that actually has something to do with power generation. (I have no doubt that achieving combustion/ignition is useful for NIF's real purpose, which is to simulate H-bomb physics to aid in maintaining our stockpile of city-destroying weapons - they have in fact created a nano H-bomb).

> This experiment didn't prove you could get more energy out of a fusion burn than you put in.

Haven't H-bomb tests already proven that beyond all doubt?

I think he meant _useful_ energy. Is it so surprising that HN is primarily interested about civilian applications and cynical when none are in foreseeable future?

The existence of stars already did. This is more like "it's plausible to do so in a reactor that won't destroy itself". The "that won't destroy itself" part is what this demonstrates, but annoyingly reporting often shortens it to the "is plausible to do so" part.

Except... correct me if I'm wrong here... The "reactor" did destroy itself.

> The fuel and canister get vaporized within a few billionths of a second during the experiment. Researchers then hope their equipment survived the heat and accurately measured the energy released by the fusion reaction.

It didn't necessarily blow up like a fusion bomb, but the energy was hardly produced in any sort of sustainable, ongoing form that we can harvest.

Worse - it's not even just the chamber that essentially destroys itself - the lasers that create the event also damage themselves: https://lasers.llnl.gov/news/controlling-backscatter-damage-...

Yeah, I really meant in a controlled reaction situation. Should have been more clear.

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