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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

#221

Post by LarryMullins »

DennisP wrote: post #148
HPsquared wrote: post #138

Earlier quoted context omitted.

That was already proven in weapons tests in the 1950s (e.g. https://en.m.wikipedia.org/wiki/Castle_Bravo ). The hard part is always building the machine to produce net energy gain, which is still 2+ orders of magnitude away.

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.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#222

Post by ipdashc »

donquixote25 wrote: post #209
walnutclosefarm wrote: post #185

Earlier quoted context omitted.

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 absor…

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".

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#223

Post by LarryMullins »

denton-scratch wrote: post #80
rgmerk wrote: post #31

Earlier quoted context omitted.

It might guarantee clean fusion power, but there's no guarantee it would be in any way economic. Edward Teller proposed something along these lines with conventional two-stage nuclear explosives back in the 1970s, but it was rapidly abandoned as horribly inefficient and costly: https://en.wikipedia.org/wiki/Project_PACER I know this stuff is fun to speculate about but the boring and unsexy option of more solar panels…

> clean fusion power From what I understand, practical routes to fusion all produce a lot of fast neutrons, and tritium. The neutrons make the surrounding equipment radioactive, and create toxic elements. The tritium is itself toxic, and is hard to contain. And the high neutron flux means that such a machine could easily be used to create weapons-grade plutonium, by irradiating uranium. And come decommissioning time,…

All of what you say is true. But on the plus side, you don't have the transuranic waste. Transuranic waste is the worst waste, the most dangerous and the most expensive and vital to store properly.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#224

Post by college_physics »

well, we have a serious energy addiction problem as large parts of the population got used to unsustainably high per-capital energy lifestyles (basically burning fossil fuel repositories like there is no tomorrow). so any paths to clean energy production are worth pursuing - provided they don't create an illusory sense of comfort and unsubstantiated hope that some fancy tech will solve everything.

fundamentally though, one would think that trying to create artificially solar interior conditions on Earth while the planet is literarily drenched in sunlight is not the shortest path to energy salvation. Life has invented already several ways to harness that energy and we have invented a few more in the meantime. I think the odds are that we will have more (as in: sufficiently) efficient harnessing of solar energy long before we create locally little suns to play with.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#225

Post by idiotsecant »

jliptzin wrote: post #163
HPsquared wrote: post #97

Earlier quoted context omitted.

Parent was basically saying it has not been a physics problem for decades, it's already an engineering problem and there is no change there. The physics are known to work and have been demonstrated decades ago in a different engineering context (i.e. weapons).

Didn’t we already know it’s just an engineering problem by virtue of the sun existing?

Boy, the HN pedantry is potent this morning.

The fact that black holes exist does not mean that we can spin one up to harvest it's hawking radiation for power. It's not just an engineering problem. That's not what that phrase means.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#226

Post by donquixote25 »

ipdashc wrote: post #222
donquixote25 wrote: post #209

Earlier quoted context omitted.

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,…

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.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#227

Post by monetus »

maria2 wrote: post #198
serioussecurity wrote: post #190

Earlier quoted context omitted.

Not to diminish the achievement, but not making that graph log scale was deeply dishonest.

How is it dishonest?

A log curve, rather than linear, would make the bars in the center taller and not give the same appearance of a massive change in the measurement. Not for me to say, but I'm guessing that, as is, it doesn't represent the work put into the effort as well as possible.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#228

Post by WhitneyLand »

rob74 wrote: post #43

Still 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,…

Major breakthrough is a subjective term so it’s hard to argue that precisely, but is it a major milestone on the way to commercial fusion, or “historic” as Dr. Kuranz says in the article? I can accept that. In 50 years, I’d guess it’ll be described in Wikipedia in such as way.

Secondly I’m not sure what you mean by saying this experiment has only academic differences with a thermonuclear weapon. It seems the only similarity is they both generate a fusion reaction. The latter is essentially multiple bombs strapped together which is quite different practically.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#229

Post by zardo »

walnutclosefarm wrote: post #185
dotnet00 wrote: post #120

Earlier quoted context omitted.

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…

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 absor…

> 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?

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#230

Post by maria2 »

monetus wrote: post #227
maria2 wrote: post #198

Earlier quoted context omitted.

How is it dishonest?

A log curve, rather than linear, would make the bars in the center taller and not give the same appearance of a massive change in the measurement. Not for me to say, but I'm guessing that, as is, it doesn't represent the work put into the effort as well as possible.

Yes, that's what a log scale does to a graph. But why do you feel a log scale is appropriate in this situation? To me, a linear scale is a much better choice. The underlying data isn't necessarily exponential, so there isn't a compelling reason to use a log scale.
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