Nuclear physicist explains why fusion ignition is hailed as a major breakthrough • Hacker News Board

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

#211

Post by scythe » Mon, Dec 19, 2022, 5:04 PM UTC

TheOtherHobbes wrote: post #76

danbruc wrote: post #59

Earlier quoted context omitted.

For one, it's theoretically impossible to make lasers 102 times more efficient, especially if you consider the current industrial efficiency of up to 20% (30% under special conditions). That is not true. You can of course not make a 10 % efficient laser more than 10 times more efficient, but there is no limit to how much more efficient you can make a laser in general, you just have to start with an inefficient enough…

I'm not sure if it's theoretically impossible. But it's certainly an incredible challenge to build a high efficiency laser system that can consistently generate many pulses per second without degrading either the laser head itself or any associated micro-focussing optics. Can we stop pretending this isn't about nuclear weapons research and - basically - continued funding? LLNL is at least a decade behind its initial…

>Can we stop pretending this isn't about nuclear weapons research

The laser practicality issue that prevents this from directly becoming a power source would also be a major barrier to its application as a weapon. The laser fires in the UV-B (351 nm), which is scattered and attenuated by air, to say nothing of smoke or dust; it also requires incredibly high targeting precision (I ascribe a small possibility to its utility as a weapon in space, but practically zero on Earth without other major developments.

>I'm sure LLNL know the maximum theoretical fusion gain for a realistic pellet design, and it's worth nothing that that number hasn't been mentioned anywhere.

I wouldn't be so sure. Fusion is in general quantum chromodynamics, which is not so well characterized (being the subject of the famous YM mass gap conjecture). Even in this case it was stated that the yield exceeded expectations and damaged the sensors, which was probably not desired.

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

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Post by LarryMullins » Mon, Dec 19, 2022, 5:13 PM UTC

thereddaikon wrote: post #166

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…

Because we've been told for decades that commercial fusion plants are a decade away. So people are understandably cynical about it. Really, physics has had a problem of late over hyping things that don't impact people's lives. Maybe that's unfair to expect every discover will directly lead to noticeable changes in technology. But I would argue that researchers over estimate how much people care about their discoverie…

> Because we've been told for decades that commercial fusion plants are a decade away.

Even if you take the most breathless headlines about NIF at face value, we are obviously still decades away from a commercial fusion power plant. Let's say laser fusion is great and perfect, all we need to do is design a commercial facility that uses modern lasers and then construct it, with commercial turbines/etc, as well as commercial production of the fuel pellets. Just that will take decades. Even basic bitch coal power plants take several years to construct and there's nothing novel about those.

But the reality is that even with the best lasers available today, they wouldn't get enough energy out to make this commercially viable. Decades more development time is needed before they can even think about designing a commercial power plant.

No sooner than 50 years.

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

#213

Post by mikeyouse » Mon, Dec 19, 2022, 5:14 PM UTC

corille wrote: post #200

mikeyouse wrote: post #174

Earlier quoted context omitted.

The 300 million joules to produce 2 million joules was almost entirely due to 2->3” implies. Some labs are already working with 20% efficient lasers, so hypothetically, Fusion is closer to “10->2->3” which is just amazing.

There are different kinds of lasers. Last time I checked in 2018, Nd:glass lasers were the only choice for producing short, ultra-high power laser pulses with regular beam profile. Beam profile is very important for tight focusing. They may be 80's technology but these were produced in 2005. Efficient fiber optic lasers were already available but they are not suitable for the task. https://lasers.llnl.gov/about/how-n…

So the NIF spec'ed out a replacement using a diode-pumped Yb:SFAP laser that they estimated to be 10% efficient in ~2009:

https://en.wikipedia.org/wiki/Mercury_laser

https://www.laserfocusworld.com/test-measurement/research/ar...

The second link has more details, but they show a 0.7% efficient NIF vs. a 7% efficient Mercury laser in the tiny little chart graphic -- which would reduce the energy for this experiment from 285MJ to 28MJ. This is way outside my area of expertise, but from what I understand, the same general tech that LLNL used to generate the HAPLS for Europe's laser research could be applied to the Mercury-like lasers and increase efficiency even further.

https://www.techbriefs.com/component/content/article/tb/insi...

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

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Post by mlyle » Mon, Dec 19, 2022, 5:15 PM UTC

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?

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 fusion for energy generation on Earth. Inertial confinement fusion ignition (and to a lesser extent, thermonuclear weapons) strongly suggest this is possible.

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

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Post by lazide » Mon, Dec 19, 2022, 5:18 PM UTC

Robotbeat wrote: post #193

lazide wrote: post #179

Earlier quoted context omitted.

Uh no. For sure, you can’t even consider the possibility of a fusion power plant without the core reaction producing power. That they figured out how to do the energy equivalent of getting the coal to actually light (finally!) in this context, is indeed useful. But it is a tiny, tiny step towards an actual working fusion power plant. And it does nothing to fix the economic issues here in competition with all the othe…

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 we’d find it worthwhile to do.

But there are literally hundreds more steps just as critical with no known solution, that are likely just as hard before we could actually have net positive energy even in a lab for such a reactor. Even if we found the economics would pan out.

That’s why I’m saying it’s a small step and we’ve got miles to go - because we do.

You’re pointing out some of the next small steps.

But those won’t get us to even having the energy balance positive on paper.

making lasers 100x more efficient for one being a notably hard problem, from a physics perspective. Probably even harder than IC fusion. The planned upgrades to lasers will help, but not enough to be close to a positive energy balance.

If the ‘first 90% takes 90% of the time’, we’re now at 2% of that first 90%. But everyone is hyping it up as we just completed it. Which is not true at all.

Honestly, it sounds like a Hail Mary funding push to try to get a new project funded or stop the lab from being shut down.

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

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Post by eitland » Mon, Dec 19, 2022, 5:26 PM UTC

lazide wrote: post #159

mikepurvis wrote: post #116

Earlier quoted context omitted.

Pumped hydro has been a concept for a while now for grid storage of power; one of the limitations of it is just the rather unique geography required. Most places with adjacent reservoirs and enough vertical separation between them also have cottages, roads, and other infra that make it hard to be constantly draining and filling.

It’s less that (IMO) - cottages and roads are usually not as dense on steep hillsides and the like, though of course they can’t be ignored entirely. The pipes involved are usually not the big issue, and the pumping ops are usually not the big issue either. The business model for pumped hydro requires relatively low cost to be economic and if it requires building a giant concrete water retention systems on top of larg…

Or you can use multiple ordinary hydro power dams (i.e. ordinary lakes where one or more outlets are blocked).

I'm fairly certain we have these multi level semi natural systems here in Norway, but I am not sure if we use them for pumped hydro.

(Og course, if one doesn't care about ecology, one of those levels can be the sea.)

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

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Post by lazide » Mon, Dec 19, 2022, 5:28 PM UTC

eitland wrote: post #216

lazide wrote: post #159

Earlier quoted context omitted.

It’s less that (IMO) - cottages and roads are usually not as dense on steep hillsides and the like, though of course they can’t be ignored entirely. The pipes involved are usually not the big issue, and the pumping ops are usually not the big issue either. The business model for pumped hydro requires relatively low cost to be economic and if it requires building a giant concrete water retention systems on top of larg…

Or you can use multiple ordinary hydro power dams (i.e. ordinary lakes where one or more outlets are blocked). I'm fairly certain we have these multi level semi natural systems here in Norway, but I am not sure if we use them for pumped hydro. (Og course, if one doesn't care about ecology, one of those levels can be the sea.)

Of course, and they are. They are even more limited in quantity, geologically.

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

#218

Post by mikeyouse » Mon, Dec 19, 2022, 5:30 PM UTC

Vt71fcAqt7 wrote: post #202

mikeyouse wrote: post #174

Earlier quoted context omitted.

The 300 million joules to produce 2 million joules was almost entirely due to 2->3” implies. Some labs are already working with 20% efficient lasers, so hypothetically, Fusion is closer to “10->2->3” which is just amazing.

Can you point me to somewhere to read more about this? Also from wikipedia: "NIF hosts the world's most energetic laser."[0] Is that true and if so can many less powerful but more efficient lasers make up for it? [0] https://en.wikipedia.org/wiki/National_Ignition_Facility#

The total energy consumed isn't what these places are optimizing for. LLNL/NIF "invented" a lot of this research so their facility is the most energetic but also ~the least efficient, while being the most important in the world. When they constructed their laser facility in 1996, NIF used the surest-bet laser system acknowledging that hypothetical competing systems could be better suited (solid state lasers were just coming into play at the time due to semiconductor manufacturing). They've done a massive amount of work ramp up the power and get their Since a lot of modern laser research now overlaps with advanced semiconductor manufacturing, the competing systems are now much more mature. Here's a good rundown, but experts think that it's plausible to use even up to 20% efficient systems. Rather than using the laser to first generate xrays - these "direct drive" systems deposit the energy from the lasers directly on the pellets.

https://physicstoday.scitation.org/do/10.1063/pt.6.2.2021102...

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

#219

Post by eitland » Mon, Dec 19, 2022, 5:35 PM UTC

lazide wrote: post #217

eitland wrote: post #216

Earlier quoted context omitted.

Or you can use multiple ordinary hydro power dams (i.e. ordinary lakes where one or more outlets are blocked). I'm fairly certain we have these multi level semi natural systems here in Norway, but I am not sure if we use them for pumped hydro. (Og course, if one doesn't care about ecology, one of those levels can be the sea.)

Of course, and they are. They are even more limited in quantity, geologically.

Yep, but just needs enourmous amounts if construction, not insane amounts.

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

#220

Post by valine » Mon, Dec 19, 2022, 5:39 PM UTC

walnutclosefarm wrote: post #157

bawolff wrote: post #39

Everything 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.

Exactly. If there was a breakthrough at all, it in 2021, when NIF finally reached the point of "burning plasma." But breakthrough, or milestone, I fear it may all be for naught. The improvements over the last two years are essentially all due to changes in the hohlraum geometry and preparation. All good, if your goal is to get burning plasmas to study. But NIF is orders of magnitude away from anything useful for powe…

The lasers were designed in the 90s and are nowhere near state of the art. Modern lasers use in semiconductor manufacturing are far more efficient.