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Usual caveat about all fusion "got more energy out than we put in" stories: https://backreaction.blogspot.com/2021/10/how-close-is-nuclear-fusion-power.html htt

by hannob 4y ago

Usual caveat about all fusion "got more energy out than we put in" stories: https://backreaction.blogspot.com/2021/10/how-close-is-nuclear-fusion-power.html https://backreaction.blogspot.com/2021/10/how-close-is-nucle... From a quick skimming it seems only one of the experts quoted here even mentions that (Tony Roulstone). (Update: i wrote this comment in response to another story and the comment got moved here, so it lost a bit of context https://news.ycombinator.com/item?id=33958678&ref=upstract.com https://news.ycombinator.com/item?id=33958678&ref=upstract.c... - the press release indeed does mention this caveat, but many news stories missed it)

whimsicalism 4y ago
> all fusion "got more energy out than we put in" I'm curious - given that this is the first time we have ever done this (even with the constrained definition as discussed in this article), how there can be a '"usual caveat" about all of the "got more energy out than we put in" stories'? AFAICT, this is the first such "story" to have ever happened artificially in history.
- guelo 4y ago
  The caveat still applied when experiments reported energy gains below 1.0.
- idlewords 4y ago
  Because all the interest of these stories is in fusion as a source of energy, and there's a long history of declaring we're near to break-even by leaving the most energy intensive part of the apparatus out of the equation. With no disrespect to the researchers in this experiment, it's not like we're surprised that fusion works or that a pellet can generate more power than is put in.
- kelnos 4y ago
  Because people like to shit on fusion, sometimes understandably so, after decades of over-promising and under-delivering. It's annoying and tiring, but there we have it. Yes, it's true that in this case we didn't actually "get more energy out than we put in" when considering the full closed system, but the point of this research was to see if they could get more energy out of the reaction itself than was put into it by the lasers themselves. Presumably the next step is to see how far they can push this, still without bothering to think about the energy needed to power the lasers themselves, because, again, that is not the purpose of this research. There are other people working on making lasers more efficient, and the overall project will benefit from that research (and so will the NIF, if they decide it's worthwhile to upgrade their 90s-era lasers to something modern). I think a lot of people here are having knee-jerk reactions and didn't read the article where they very clearly explain the caveat and what the researchers actually did.
  - whimsicalism 4y ago
    To be fair to the original commentator, their comment was moved from a different article where it was not so clearly explained.
operator-name 4y ago
"That’s because they had to use 500 MJ of energy into the lasers to deliver 1.8 MJ to the target – so even though they got 2.5 MJ out, it’s still far less than the energy they needed for the lasers in the first place. In other words, the energy output (largely heat energy) was still only 0.5% of the input."
- eloff 4y ago
  I don't see that scaling anytime soon, still more than two orders of magnitude away. But never say never.
  - jerf 4y ago
    The exact numbers depend on the form of fusion in question, but fusion does have some several places where it has quite substantial x^n growth possibilities, where "n" is definitely greater than one and can be greater than two at times, sometimes even substantially so. This means that there is some real, concrete hope for improvement in a way that, say, solar could never improve more than 4-5x where it is now because the absolutely best it could ever hope for is 100% efficiency. At the core, this is because as you get the plasma hotter and more confined, the rate of fusion goes up very quickly, much much beyond linear increases.
    - eloff 4y ago
      This is laser based fusion, which is super cool, but it might be a stretch to expect 200x more efficient lasers. Still maybe there's other things you could do, like make a bigger fusion reaction. Hydrogen bombs do it, so maybe.
      - zbobet2012 4y ago
        The lasers they use today are 20x less efficient than state of the art. The capacitors are also massively less efficient. So they only "need" to drive the Q factor of the reaction up by ~5x to be positioned to build something with a net energy gain. Because of the physics of fusion (or ICF) returns on power are non linear. It's very much possible research here results in a path to a "net gain facility".
alephnil 4y ago
And they mention this right in the press release. Quote: “The Lawrence Livermore National Laboratory experiment shows that scientists can get more energy out than put in by the laser itself. This is great progress indeed, but still more is needed: first we need to get much more out that is put in so to account for losses in generating the laser light etc (although the technology for creating efficient lasers has also leapt forward in recent years). Secondly, the Lawrence Livermore National Laboratory could in principle produce this sort of result about once a day – a fusion power plant would need to do it ten times per second. However, the important takeaway point is that the basic science is now clearly well understood, and this should spur further investment. It is encouraging to see that the private sector is starting to wake up to the possibilities, although still long term, of these important emerging technologies.” While this spins it in an optimistic way, the challenges to make this work are significant. The laser is quite inefficient, so the gain must be much much larger before you have net energy gain. To scale it up to implode a capsule tens of times a second rather than a few times a day, is in the order of 100.000 times more frequent than today.Thus this is a long way from commercial production.
- zbobet2012 4y ago
  The NIF uses lasers produced in the 90's because their core mission isn't to make lasers better. We already have lasers which are 20x more efficient, and hitting a pellet 10*s is a trivial task. Those lasers can fire a 1khz or better. The EUV light sources for semiconductor lithography do this tens of thousands of times a second. The goal of the research being done at NIF is to understand inertial confinement fusion. "Solving" these other problems isn't as important, other folks are solving these all day long for commercial industries already.
deleted 4y ago
[deleted]
tunesmith 4y ago
So... Q-plasma is above 1 for the first time, which is a huge deal. Q-total is still below 1, but some of that can be improved through already-known laser efficiency advancements, and also by pushing Q-plasma higher. I think pushing Q-plasma above 1 is the big gate though, isn't it? I mean, partly psychologically. Showing that it's actually technically possible.
- pfdietz 4y ago
  It's not really a big deal, since laser fusion needs Q of 500 to 1000 to actually make sense.

by hannob 4y ago

whimsicalism 4y ago

> all fusion "got more energy out than we put in" I'm curious - given that this is the first time we have ever done this (even with the constrained definition as discussed in this article), how there can be a '"usual caveat" about all of the "got more energy out than we put in" stories'? AFAICT, this is the first such "story" to have ever happened artificially in history.

guelo 4y ago
The caveat still applied when experiments reported energy gains below 1.0.
idlewords 4y ago
Because all the interest of these stories is in fusion as a source of energy, and there's a long history of declaring we're near to break-even by leaving the most energy intensive part of the apparatus out of the equation. With no disrespect to the researchers in this experiment, it's not like we're surprised that fusion works or that a pellet can generate more power than is put in.
kelnos 4y ago
Because people like to shit on fusion, sometimes understandably so, after decades of over-promising and under-delivering. It's annoying and tiring, but there we have it. Yes, it's true that in this case we didn't actually "get more energy out than we put in" when considering the full closed system, but the point of this research was to see if they could get more energy out of the reaction itself than was put into it by the lasers themselves. Presumably the next step is to see how far they can push this, still without bothering to think about the energy needed to power the lasers themselves, because, again, that is not the purpose of this research. There are other people working on making lasers more efficient, and the overall project will benefit from that research (and so will the NIF, if they decide it's worthwhile to upgrade their 90s-era lasers to something modern). I think a lot of people here are having knee-jerk reactions and didn't read the article where they very clearly explain the caveat and what the researchers actually did.
- whimsicalism 4y ago
  To be fair to the original commentator, their comment was moved from a different article where it was not so clearly explained.

operator-name 4y ago

"That’s because they had to use 500 MJ of energy into the lasers to deliver 1.8 MJ to the target – so even though they got 2.5 MJ out, it’s still far less than the energy they needed for the lasers in the first place. In other words, the energy output (largely heat energy) was still only 0.5% of the input."

eloff 4y ago
I don't see that scaling anytime soon, still more than two orders of magnitude away. But never say never.
- jerf 4y ago
  The exact numbers depend on the form of fusion in question, but fusion does have some several places where it has quite substantial x^n growth possibilities, where "n" is definitely greater than one and can be greater than two at times, sometimes even substantially so. This means that there is some real, concrete hope for improvement in a way that, say, solar could never improve more than 4-5x where it is now because the absolutely best it could ever hope for is 100% efficiency. At the core, this is because as you get the plasma hotter and more confined, the rate of fusion goes up very quickly, much much beyond linear increases.
  - eloff 4y ago
    This is laser based fusion, which is super cool, but it might be a stretch to expect 200x more efficient lasers. Still maybe there's other things you could do, like make a bigger fusion reaction. Hydrogen bombs do it, so maybe.
    - zbobet2012 4y ago
      The lasers they use today are 20x less efficient than state of the art. The capacitors are also massively less efficient. So they only "need" to drive the Q factor of the reaction up by ~5x to be positioned to build something with a net energy gain. Because of the physics of fusion (or ICF) returns on power are non linear. It's very much possible research here results in a path to a "net gain facility".

alephnil 4y ago

And they mention this right in the press release. Quote: “The Lawrence Livermore National Laboratory experiment shows that scientists can get more energy out than put in by the laser itself. This is great progress indeed, but still more is needed: first we need to get much more out that is put in so to account for losses in generating the laser light etc (although the technology for creating efficient lasers has also leapt forward in recent years). Secondly, the Lawrence Livermore National Laboratory could in principle produce this sort of result about once a day – a fusion power plant would need to do it ten times per second. However, the important takeaway point is that the basic science is now clearly well understood, and this should spur further investment. It is encouraging to see that the private sector is starting to wake up to the possibilities, although still long term, of these important emerging technologies.” While this spins it in an optimistic way, the challenges to make this work are significant. The laser is quite inefficient, so the gain must be much much larger before you have net energy gain. To scale it up to implode a capsule tens of times a second rather than a few times a day, is in the order of 100.000 times more frequent than today.Thus this is a long way from commercial production.

zbobet2012 4y ago
The NIF uses lasers produced in the 90's because their core mission isn't to make lasers better. We already have lasers which are 20x more efficient, and hitting a pellet 10*s is a trivial task. Those lasers can fire a 1khz or better. The EUV light sources for semiconductor lithography do this tens of thousands of times a second. The goal of the research being done at NIF is to understand inertial confinement fusion. "Solving" these other problems isn't as important, other folks are solving these all day long for commercial industries already.

deleted 4y ago

[deleted]

tunesmith 4y ago

So... Q-plasma is above 1 for the first time, which is a huge deal. Q-total is still below 1, but some of that can be improved through already-known laser efficiency advancements, and also by pushing Q-plasma higher. I think pushing Q-plasma above 1 is the big gate though, isn't it? I mean, partly psychologically. Showing that it's actually technically possible.

pfdietz 4y ago
It's not really a big deal, since laser fusion needs Q of 500 to 1000 to actually make sense.