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Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
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Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#272Earlier quoted context omitted.
> What most surprised me about NIF's ignition announcement was that this was even news. I'd assumed for years that most if not all tokamaks and stellerators could already achieve at least some brief fusion, just not to a useful degree. I think they've done fusion in tokomaks and stellerators before, it's just that the energy applied to the plasma is greater than the additional energy that's created by fusion. It's no…
I'm not sure if it's true or not exactly, but I don't see how the NIF experiment would be any different from that if that were true, and in that case it wouldn't be news at all. It's not like they didn't use absurd amounts of laser power to get a tiny poof.
Going from a Qplasma of 0.9 to 1.5 for inertial confinement fusion seems like a step-change to me. For gains greater than one you have a positive feedback mechanism going for you -- the fusion you create makes more and bigger fusion. It is the difference between a tiny little bomb that works or doesn't work. It's this positive feedback that make scaling up potentially "easier". That's why it is a breakthrough, and concerns about lasers, etc. seem to be getting the cart before the horse. On the other hand, for magnetic confinement fusion, going from the same Q=0.9 to Q=1.5 is a much more "meh" event. I can see why some people are concerned about "where to draw the line" about total energy consumption, if it were MCF we were talking about. Maybe people have the expectation that ICF is further along the learning curve than it actually is? That's not to say that ICF is going to be viable for commercial fusion reactors in future. There are still many, many hurdles to cross. And maybe they will never be crossed for financial reasons.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#273Earlier quoted context omitted.
The reason it looks that far away is that NIF uses lasers from the 1990s with only 0.5% efficiency. Equivalent modern lasers are over 20% efficient, which would put overall net energy gain only one order of magnitude away. https://physicstoday.scitation.org/do/10.1063/pt.6.2.2021102...
> which would put overall net energy gain only one order of magnitude away. With modern lasers they would be closer to Q=1 without the funny energy accounting. But still several orders of magnitude away from commercially viable, which requires vastly greater efficiency than Q=1.
Energy return on investment. Some oil extraction is currently at EROI=10, assuming EROI and Q can be made to be the same concept. Higher than EROI=50 is unheard of today, even 40 is pretty rare. EROI for this fusion method would be ~0.015.
The worst fusion methods scales with the cube of the radius of the area that can be made to fuse. So we "only" have to get a 10x bigger area to fuse, or have the same area fuse for 10x longer (and make the facility not blow up or melt down from doing that).
Working fusion is surprisingly close.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#274Earlier quoted context omitted.
I would consider the sparking of fire a big step. And that it used inefficient lasers is irrelevant because it wasn’t intended to be anything but a demonstration of ignition and scientific breakeven. The follow-ons which would use modern efficient solid state lasers were delayed because there’s no reason to build a power plant without first having the fire. Funding for them was premature, and it was right to focus on…
This isn’t sparking fire. We already know how to do that. Fusion reactors have been doing that for decades, and we’ve been doing it overall for 80ish years now. It’s sparking fire in a very specific synthetic scenario which maybe could be useful in making a specific type of fusion reactor. It’s a critical step, yes, in development of that type of reactor, if we wanted to do so. Currently there is no reason to believe…
NO. The lasers are immaterial. You could use a hammer to cause the initial fusion (in fact ... [1]). The point of ignition is to have fusion powered by fusion, NOT by lasers. We want fusion of two atoms cause at least 2.000001 other atoms to fuse, and then raise that number. Not even by much 3 will definitely do it. If Q > 1, then this must have happened, there is no other explanation. That's the big advance. The point is to have the fire burn after we've lit the match.
You want to use lasers to initiate some fusion, you can do that using a tabletop laser lab (although magnetic confinement and big voltages is much simpler).
So this is the first machine where we're sure: it wasn't fusion caused by lasers, it was fusion caused by neutron pressure! Where did that neutron pressure come from? From other atoms fusing!
Note also that the sun does NOT do this. Fusion inside the sun is powered by falling atoms converting their falling energy first into heat then into singular fusion events, which essentially explode and throw a lot of atoms back up. Then the cycle begins again. Fusion inside the sun is a self-limiting reaction, which is why stars don't just blow up once, but "burn" over a long time. All the fusion inside the sun really does is slow down gravity for a little bit, then immediately stop. Gravity is producing the heat from the sun.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#275Still unconvinced why this is such a major breakthrough - it may be the first net-positive controlled fusion, but the distinction between controlled and uncontrolled fusion is a bit academic in this case. In uncontrolled fusion ( https://en.wikipedia.org/wiki/Thermonuclear_weapon ), you are using a nuclear fission primary stage to generate enough energy to start the fusion reaction in the secondary stage. In the NIF,…
You greatly underestimate the order of magnitude difference of produced energy in these two examples. You can't contain a bomb's hydrogen fusion reaction in a chamber for the simple reason that you need a nuclear fission warhead just to ignite it. So if you want to produce useful, controlled energy outside of killing things, the lasers are your only shot for inertial confinement fusion. Yes they still get damaged, bu…
Well, you can at least power space ships with it via the Orion drive. :)
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#276Earlier quoted context omitted.
This isn’t sparking fire. We already know how to do that. Fusion reactors have been doing that for decades, and we’ve been doing it overall for 80ish years now. It’s sparking fire in a very specific synthetic scenario which maybe could be useful in making a specific type of fusion reactor. It’s a critical step, yes, in development of that type of reactor, if we wanted to do so. Currently there is no reason to believe…
NO. The lasers are immaterial. You could use a hammer to cause the initial fusion (in fact ... [1]). The point of ignition is to have fusion powered by fusion , NOT by lasers. We want fusion of two atoms cause at least 2.000001 other atoms to fuse, and then raise that number. Not even by much 3 will definitely do it. If Q > 1, then this must have happened, there is no other explanation. That's the big advance. The po…
The hohlraum is destroyed almost instantly by the reaction.
The reaction is initiated by the lasers.
You can’t actually use a hammer to initiate it at any useful scale because hammers can’t create the appropriate pressures and temperatures to initiate the process at the scale needed to produce a useful energy output. Which is why the lasers.
So no, the lasers are not immaterial at all.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#277We already have a stable fusion going. It's 8 light minutes away. All you have to do is to point a solar panel at it to harvest the energy.
Gravity confinement fusion with optical coupling. Really much, much more practical than the fanciful notion that NIF will miraculously lead to a commercial energy source that ingests diamond-coated nanopellets and has a duty cycle of 1:1e15.
NIF is probably a dead end for fusion power, but this is still an important milestone.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#278I can tell you that regular people took the announcements as a sign that nuclear fusion as a real useful thing is imminent, and couldn't be convinced otherwise! But then if your announcements are completely rational you don't get as much funding. A lot of us nerds on HN don't like it when people do propaganda, but I assume we also like to win, right?
When people have been doing the propaganda for longer than I have been alive, I become an old, salty fucker.
I recall reading an old 60s issue of 'Physics Today'; someone prophesized fusion ws 20 years away.
None of that in the (look, it's still around) recent article. Insightful details are present. And some honesty ... e.g.
"The agency toned down the ignition objective, emphasizing NIF’s ongoing experiments to investigate materials’ behavior under extreme densities and pressures in support of nuclear stockpile maintenance."
[https://physicstoday.scitation.org/do/10.1063/PT.6.2.2022121...]
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#279Everything i have heard about this makes it sound more like a milestone than a breakthrough. I.e. its great it happened and an important step, but its not shocking that we eventually did it. When i hear breakthrough i think of something more unexpected. I.e. figuring out how to solve a problem we had no idea how to solve.
I feel like HN is being especially pedantic and jaded about this specifically and I don't really get why. Scientifically this is absolutely a breakthrough, just like the detection of the Higgs boson was despite them already having expected it or just like LIGO's detections of gravitational waves were despite that being entirely what it was built for or just as JWST's detections of galaxies much older than those seen…
Milestones can be impressive too.
I think the distinction is that with a breakthrough there is something new to learn, where a milestone you basically say "good job, keep up the good work". With a breakthrough there is more content to engage with because you can try and understand what is new. A milestone is great, but there isn't anything new to really engage with, so it has a shorter news cycle.
As a comparison - stable diffusion is a breakthrough - we are still trying to figure out what it all means and how it will or wont change society. its been months now and we are still talking about it. We wont be talking about this fusion thing months from now. That doesn't mean its less important only a different type of event.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#280Earlier quoted context omitted.
Didn’t we already know it’s just an engineering problem by virtue of the sun existing?
Ordinary hydrogen-hydrogen fusion in the sun only works because the sun is so freakin' huge. It's so unlikely even under the sun's massive gravitational and heat that the power output is about 270W/cubic meter-- compare to human metabolism or an energetic compost pile, which is over 1000W/cubic meter. We actually have to do a whole lot better than the sun, under far less favorable conditions-- to have practical fusio…
Interesting, didn’t know that!