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Comment by sillysaurusx | Hacker News Reader

This tweet claims that 500MJ of energy was required: https://twitter.com/latzenpratz/status/1602686252486217728

> "had to put 500 megajoules of energy into the lasers to then send 1.8 megajoules to the target - so even though they got 2.5 megajoules out, that's still far less than the energy they originally needed for the lasers," says Tony Roulstone of the University of Cambridge.

But it's good to finally see progress. Very few technologies can transform the world the way a practical fusion reactor could.

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It was discussed a lot in the threads about this yesterday, but apparently the lab had relatively inefficient lasers. Newer ones are an order of magnitude more efficient

This is what I captured from the press conference:

300 megajoules was used to generate the laser (this is also captured in [1]). They also mentioned that newer lasers have 20% wall plug efficiency. If so, they need to improve the energy output by 5x in order to break even relative to wall plug energy consumption.

[1] https://techcrunch.com/2022/12/13/world-record-fusion-experi...

“Wall plug energy consumption”

I don’t know why but this caused me to picture Alec from Tech Connections in a few years time, showing off his fusion laser plugged in to a kill-a—watt, while he explains carefully, through the magic of buying two of them, why you can get more power out than you put in, and why these old inertial confinement fusors were pretty neat actually.

That's just the lasers, the rest of the plant needs power too. Big water pumps are big power hogs, as is the rest of the supporting equipment that any power plant requires to operate. Far over "wall plug" break even is required for commercial viability.

Just bootstrap a second fusion power plant with the first, then continue on, similar to how compilers for a language can be written in the language itself.

Bootstrapping the power plant isn't the problem. The economics of the power plant are the problem, naming producing a worthwhile surplus of power, after accounting for all the power needed by the plant itself.

So if we had the 20% wall plug efficiency, then we need that 3.2:2 ratio to become 10:2 to hit break-even. That looks like a huge gap but maybe there are tricks here that resolve this once you get over the initial gap.

That’s only because they’re using old school flash pumped lasers, not the new solid state lasers you’d use today if you wanted to make a power plant demo.

Can solid state lasers produce the high energy needed here?

Yes. https://en.wikipedia.org/wiki/Laser_Inertial_Fusion_Energy#M...

I'm not really seeing any convincing numbers there. Mercury lasers seem to only be 10% efficient. I get that this is better than the lasers that were just used at NIF, but that still seems pretty far from useful.

It’s useful enough to produce significant net energy if they continue with the gain scaling that ignition allows.

It just seems a little strange to take credit for a milestone when the milestone everyone cares about is yet to be reached. (More energy out than in.)

Good to hear that there's a laser design that might achieve that.

It's a significant milestone because demonstrating you can get net energy from the reaction removes a lot of uncertainty of whether it's possible in the real world. It starts to turn inertial fusion into an engineering problem of how you increase the efficiency of each stage.

I think the confusion here is at least partially due to most articles obscuring the primary purpose of the NIF. Its not supposed to support commercial energy development, its supposed to support nuclear weapons development under the Nuclear Test Ban Treaty, where testing bombs via setting them off is banned.

So the NIF is supposed to give a testbed to study implosion created fusion reactions that produce enough energy to "ignite", that is, propegate the reaction to the rest of a hypothetical bomb. In that case, the amount of energy needed for the infrastructure to produce the initial implosion doesn't matter, what matters is that the energy coming out is more then the actual energy that triggered the reaction, so that the hypothetical bomb would blow up and not fizzle.

Exactly! It's so strange this is somehow made to be about fusion as an energy source. I'm happy to announce that Q>>1 has already been achieved on multiple occasions. In the cores of the thermonuclear devices tested by the US and USSR in the 50s. (Unfortunately that technology proved unviable as a path to civilian fusion power.)

Don't take it too personally, but you, and many others here, need to rethink their approach. You see a short tweet without context about a topic you clearly know nothing about (which is totally, fully okay, it's a complex topic), and think you are now able to criticize milestones in this impossibly complex topic.

Not even ask questions, not something like "hey, I saw this tweet, I know it's just a tweet, but can someone help me understand context?", no, you actually go ahead and criticize work that you know nothing about, and when confronted, you double down.

On some level, you must know yourself that it might be better to ask as many unloaded questions as you want, but otherwise sit this one out in terms of assessment.

No thanks.

I get that people are emotional about this, but it’s important to treat science with a critical eye.

The claim is that more energy came out than was put in. This is false.

It’s not just me saying it. https://www.tiktok.com/t/ZTRVP5Pmg/

There is no “context” to understand. Yes, it’s an impressive feat. Yes, other laser designs might fix the huge ignition costs. But that hasn’t happened yet, and until it does, it’s completely fair to point that out.

Will it win me any friends? Probably not. It’s like showing up to a party and saying the reason for the party is mistaken. Very few people care.

But scientists should, and I am one. Doubly so for incorrect reporting to laymen. We have a responsibility to convey what was actually achieved, not what we wish was achieved.

Worth noting that the milestone achieved was positive Q_plasma (more energy out of the plasma than in).

They are using inefficient lasers because they are cheaper to buy/maintain/modify for research purposes.

Determining the conditions for positive Q_plasma is largely a matter of science/research so the external system doesn't matter as long as the variables are controlled and results are reproducible.

Once positive Q_plasma is well understood/reproducible, achieving positive Q_total (more energy produced than spent running the infrastructure) is just a matter of engineering and potentially waiting for the SOTA for components (like lasers or materials) to catch up.

TLDR: This is the scientists proving the theory. Now it's the scientists' job to refine the theory. Then the engineers get to put it into production.

The theory was proven to everybody's satisfaction in 1950.

There will be no production, except of new, smaller thermonuclear warheads. That is their legislated remit.

It is a milestone, and I do think the researchers deserve credit for that. Getting more energy out of the reaction than was delivered to it by the lasers is actually important.

No one (except perhaps poor science "reporters") is claiming that this means we now have free and cheap fusion power. Of course the energy put in to operate the lasers themselves needs to be accounted for -- and it is! -- but that doesn't make what they've achieved useless. It's also useful to remember that the researchers involved are not the people writing press releases and articles; let's not minimize their achievement just because of sloppy, sensationalist reporting.

I like the analogy downthread of a kid being excited about scoring a home run in baseball, but the dad chastising the kid for celebrating before actually winning the game. That's what it feels like is happening here.

This is a huge step in the right direction, and it should be celebrated as such.

Why are they using these "flash pumped" lasers if more efficient ones are available?

Because they are researching inertial confinement fusion, not trying to build a working power plant. The efficiency of the lasers doesn't matter, since it doesn't affect their research.

Is energy on the order of 300MJ so cheap? You’d think that cutting it down to 150MJ would allow them to do more experiments.

300MJ ~= 83kWh which is like, $2000 in CA

I think you're out by some orders of magnitude. With the current energy issues in the UK it'd be under £100. Other things suggest in California it's more like 20 cents per kWh so were you thinking ~$20?

You're right of course, messing up my units again.

300 megajoules is 83 kilowatt hours

a typical power price at trading hubs is US$40 per megawatt hour, though this varies considerably depending on many factors and is sometimes actually negative

a typical retail price is US$120 per megawatt hour

so this is about US$10 worth of electrical energy

It’s a proof of concept. Upgrading lasers that already work is not necessarily the best use of limited funds.

They could get higher power out of more efficient lasers, enabling research at higher energies or bigger targets

Not to mention the money they would save on electricity bills.

The electricity bill is like $2000. It'd waste more money for a manager to think about how to replace equipment, at California pay rates. This whole thread is making me lose faith in HN.

Actually 83 KwH costs only about $20 in CA (avg $0.25 / KwH and probably LRL pays even less.

That's not the purpose of the research, though. They are solely focusing on the energy transfer between the lasers themselves, and the output from the reaction. It's not clear that higher energies or bigger targets will teach us anything new.

Upgrading the lasers would slow the project down as new hardware is installed and issues are worked out. Not to mention I doubt the new hardware is cheap, and may be more expensive than burning excess energy using old laser tech in the meantime.

Other research groups work on laser efficiency, and the "final product" using this method (if it ever proves viable) would put together all the best pieces to get the best efficiencies.

It's a very old lab, and replacing them isn't cheap/easy.

You don't need to use efficient lasers to get the scientific results they're after - other people have already very accurately measured the properties of modern lasers, so we can predict how they would perform without having to actually use them.

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