> They got what, 2.5 megajoules out of 2.1 in?

Of laser energy into a tiny control volume that doesn't consider how much energy went into the laser systems. If you draw the control volume around the building and see that the lasers require vastly more energy than what came out, I think you'll be less excited, right?

We've been getting lots of energy out of fusion since the early 1950s with thermonuclear bombs. We know we can get energy out of a control volume. But is it a practical energy source is still the question imho.

Could you elaborate on that? What do you mean that the lasers could require more energy?

Is it that in a specific volume they got X EM energy coming in from the laser and Y thermal energy coming out, with Y>X BUT the electricity consumption of the lasers is Z>Y>X?

If so that's sort of misleading, like the plethora of claims from ITER. I hoped this was different.

Exactly. Looking at the Wikipedia article [1] suggest that they start out with 422 MJ stored in capacitors, turn this into 4 MJ IR laser light, convert it into 1.8 MJ UV laser light, this into x-rays of which 0.15 MJ heat the target of which finally 0.015 MJ heat the fuel. Depending on what in this chain you consider the input energy, you can get orders of magnitude different numbers - 15 kJ of energy produced could either be a gain of 1 or a gain of ‭0.0000036 or anything in between.‬ And this is before trying to capture the released energy and converting it into electricity, this will come with another sizable loss.

[1] https://en.wikipedia.org/wiki/National_Ignition_Facility

From https://www.ft.com/content/4b6f0fab-66ef-4e33-adec-cfc345589...

> The fusion reaction at the US government facility produced about 2.5 megajoules of energy, which was about 120 per cent of the 2.1 megajoules of energy in the lasers, the people with knowledge of the results said, adding that the data was still being analysed.

They probably upgraded the rig since the Wikipedia article was written, so most likely the 2.1 MJ refers to the UV light numbers.

If this is assumption is true, they only produced 0.6 % of the energy they spent. Another question would then be, how relevant this is, i.e. could the UV light be produced much more efficiently than the experiment does? Maybe some constraints forces them to use a very inefficient process? In that case it might be reasonable to use the UV laser power as the reference for the gain.

Sure, and if they upgrade the lasers themselves to current laser tech (as I understand it, the NIF's hardware is around 25 years out of date on that front), then that 0.6% number probably jumps to 20% or so. Which still isn't enough, but is way closer than 0.6%.

Add to that the fact that improvements in laser efficiency is a hot research area (as lasers are used commercially in a lot of places, and cost-cutting is always a concern), and this is starting to feel a little more attainable.

I think the more interesting question is "how does this scale with more laser power?"

Even if the lasers are 1% efficient does it matter if 100 GJ of electrical power results in 100 TJ of fusion heat? I'm not saying this is at all how it scales, but it is the logic behind pursuing an ICF power plant. The fuel gets ignited and heats itself.

Also, for fun, 100 TJ is 24 kT TNT equivalent: slightly more than the bombs dropped on Hiroshima and Nagasaki. Trying to capture this energy released instantaneously would be a fun engineering challenge.

Presumably they mean that there are efficiency losses in charging the supercapacitor banks used to fire the lasers; so that if you consider the system over multiple duty cycles rather than over a single cycle, it's no longer energy-positive. (I.e. if the system were capturing its emitted energy — and that emitted energy needed to be enough to act as a grid power source feeding input power to the supercapacitors, rather than merely being the equivalent of the direct output power of the lasers per shot — then it wouldn't be enough to sustain the reaction.)

But personally, I don't know whether that's actually important. Power plants usually consume a nontrivial fraction of their own produced power to power themselves, and in fact consume more than 100% of produced power when starting from a full stop — meaning that in initial few-shot conditions, even when feeding back their own produced power into themselves, they still need (huge amounts of) external power input to get going, like a car engine needing a battery + starter motor. Only a rare few kinds of power plant can be used to "black start" a power grid. Most types of generator need to overcome initial higher resistances, e.g. inertia (and thereby back-EMF resistance at the transformer) in getting heavy turbines spinning from a stop.

It wouldn't be at all strange if a practical fusion power plant turned out to be energy-negative over a few-shot run (i.e. required "bootstrapping"), but then became energy positive over a theoretical 24/7 run at whatever its optimal duty cycle is. And a single-shot run becoming net-positive would be a good point to start to consider those more practical calculations, since they'd have been useless to consider until then—a power plant can't possibly be net-positive over any kind of runtime + duty cycle, if its core reaction can't be net-energy-positive when considered in isolation.

Which is, to me, why it probably does make sense for ITER to be excited. They've reached the point where they can stop using a lab-bench model of power efficiency, and start trying to come up with another, more full-scale model of power efficiency to replace it with.

Not /u/acidburnNSA, but what was meant is that no laser is 100% efficient. Not only do they not convert 100% of their electrical input into laser energy, but they also require other support systems, notably cooling. So we need to consider the total energy costs of the building the fusion experiment is conducted in, not just the physically small area where the fusion reaction is happening inside the reactor.

Still, this is an important step in the development of fusion energy reactors.

So the laser energy that went into the reaction in the form of light is less than what came out of the reaction. However, the energy needed to produce that laser energy may be orders of magnitude more depending on the laser. AKA: the Wall Plug Efficiency.

Tabletop rigs can be as efficient as 50%, however high power such as we see here tends to come with drastically reduced efficiency.

I think fusion-plants have always been "15 years away", and most likely will be so for quite a few years...

Edit: I was wrong, fusion is always 30 years away: https://www.discovermagazine.com/technology/why-nuclear-fusi...

I don't know what people get out of repeating this on every single fusion article. It's not inventive or insightful, and it doesn't further the discussion in the slightest.

Because it is context that is rarely included in the article.

some people are new to the Fusion discussion. They've missed the last 50 yrs of "fusion is 10 yrs away" claims. Over the years, I've learned to temper all discovery excitement. Its the other side of the coin equivalent of the the XKCD 10000 comic[1].

[1] https://xkcd.com/1053/

Because it's A) true, B) relevant to keep all of the hype in check. The year of Linux on the desktop is always right around the corner too. Yes, they are tropes, but they were not born out of nothing.

Someone has to keep the bloviated PR campaigns checked with reality. Otherwise, some crazy fools might actually start believing that fusion is real and gets duped out of their money. If you can't stand a bit of real criticism, then maybe you should sell your scam somewhere else. Otherwise, take it on the chin, retool your message, and come at it honestly.

It's not true. The original quote was 30 years given current funding. They reduced the funding and surprise surprise it didn't get done. It's like when you estimate how long a project will take given a thousand people, and they reduce the number of people on the project to one person and then hold you to the original estimate.

Okay, but then if the funding has decreased, what hasn't the "years away" increased? No, that wouldn't sound good in a press release now would it. So they keep saying it is just around the corner. It's like the religious people saying that the second coming is right around the corner for over a thousand years now. I know, I know, religious zealots and science (zealots?) are different. Or are they?

Show me a fusion scientist saying fusion is 30 years away. No one in the article is even saying that. It's people in the comments repeating the same thing from the 80s.

What article? It's people speculating on the announcement that another announcement is coming. It just feeds into the hype machine. With this level of hype, watch them come out and show off the Segway!

Okay. Guess I'm done here.

If you want to keep the hype in check, do it with facts like /acidburnNSA did above. Let people debate. You don’t even know what will be announced. Repeating the same joke in every single fusion article is tiresome and has long past its funny expiration date.

Why does it have to be funny? It's just a sad statement about the situation. Maybe you're tired of people not being as excited as you, or even willing to for a second hold their breath any longer on this topic. But here we are at another announcement essentially saying "this shit is hard. with more funding, we could possibly maybe do something in the nearish future". Anything announced in the PRs is just mumbojumbo hand waving to explain why what they are saying isn't really saying anything substantive other than to keep fusion in the news so it is easier to raise money. This is the main perception of fussion by the masses.

Personally, I just don't see fusion being a viable solution for anything in any of our lifetimes. I will gladly admit how wrong I was if/when someone solves it. I just have a much stronger doubt in sci-fi vs reality, and don't get swooned by the hype machines surrounding fusion.

What is tiring to me is calling the skeptics tiring. But to each their own

I think one can be simultaneously excited about a big breakthrough like this, but also understand that there's still a ton more to do before we have viable fusion power.

And it's unreasonable and annoying to expect everyone to say "This is amazing, but..." rather than just "This is amazing". Yes, we know, fusion power isn't ready, and we have no idea when (or if) it will be.

I haven't been "holding my breath". I've been watching from afar, checking in occasionally (like when this sort of news comes out), and I genuinely think this particular breakthrough is exciting. I don't need the tiresome -- yes, incredibly, frustratingly tiresome -- legion of naysayers coming in and stating the obvious every single time.

It's also weird to watch people debate passionately but without the passion to actually gain expertise in the thing they are debating. I find it weird that we do this. I'm not immune, we all do it. We should at least be cognizant and try to reduce how heated we get over things we know so little about. It is just weird.

It's not a trope; it's a cliché. There's nothing wrong with poking holes in overinflated hype, but do they have to be so boring and repetitive about it.

It's also just a parrot trick. There's no reason behind why it is 30 years away or even why 30 instead of 15 instead of 20. It is just a line. These numbers are meaningless but touted as a way to add validity to the argument without providing actual evidence for why fusion is such a tough nut to crack. We should dispose of hype, but let's do it from a place of understanding. I hope we're a bit smarter than parrots.

If you keep telling me the same thing with the same lack of results, I could say the same to you as being boring and repetitive. Just because you say 2+2=5 and someone tells you you're wrong every time doesn't mean they are boring and repetitive.

How is this "lack of results"? This particular announcement is a huge result!

Maybe it's not the result you think it should be ("with all they hype over decades, we should have fusion power by now"), but... too bad. It is what it is, and this particular announcement is indeed impressive.

It is not, in fact, a huge result, except insofar as it is convenient for further weapons research. It does not bring civil fusion power even a single day nearer.

Not an engineer in this field, so I may have misread/misunderstood, but I read that 2.5MJ out for 2.1MJ of laser energy in, NOT the total energy needed to make the whole thing work.. So, in a layman’s world, it is not a net gain of power, only a small subset of the system yielding more power than it took in.

Happy to be proven wrong and told that it is more of a breakthrough than I think it is..

No, you are correct.

So they are ignoring the laser efficiency as well as the thermal to electric efficiency? If you did the same for a tokamak, stellerator or Bussard, would you get a similar ratio?

Jup. Fusion research is necessary and funding should be provided. But it is not close to commercial or generative viability.

So there is at the moment no working design for a generator as a plant that produces more electricity than it takes in.

Yup? Absolutely not, nothing close to this has been achieved with other reactors.

Electricity in, heat out, I think. Getting that heat back to electricity will cost some, I expect more than that 0.4

The efficiency of a thermal power plant is around 40%, depending on the temperature of the steam it can produce. https://en.wikipedia.org/wiki/Thermal_power_station#Thermal_...

Note that energy in the case of ICF is produced instantaneously. There is no approach to capture this energy in production at this moment. Capturing that enery is still ongoing research topic.

The net energy gain is very slim and has to be converted to electricity to power the lasers – in doing so, there's so much loss, it is again NEGATIVE.

It's always the same…

As it always is with new, unproven things.

or fusion.

There are always these articles: net energy gain finally! and then: no not really.

Reminds me of solar. That took a century to get to where we are today where the net energy output is much greater than the energy needed to manufacture them.

It being hard and it requiring continual progress does not mean that progress does not occur.

Correct. Nuclear fusion research should be funded and realistic goals be set.

…which is exactly what this is?

How long has humanity been working on fusion? Wasn't Ivy Mike in the early 50's? Glaciers continually progress too, but it's not obvious on human timescales.