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There is quite some misleading terminology being used in the field of nuclear fusion (see excellent overview here [1]). So I was genuinely curious what kind of

by nuccy 5y ago

There is quite some misleading terminology being used in the field of nuclear fusion (see excellent overview here [1]). So I was genuinely curious what kind of Q is used in this paper, so here it is: > In this regime, self-heating from α-particle deposition exceeds the external heating input into the DT8; this ratio is denoted Qα, where the self-heating is taken relative to the heating power to the plasma—for inertial fusion this is the PdV compressional work on the fuel and not the total laser energy (P, pressure, dV, volume change). Qα > 1 is a burning plasma. So as far as I understand such Qα > 1 can be reached without sustaining neither pressure or volume, so one can think about it as an explosion rather that intuitive burning (somewhat continuous process). To summarize: Q_total = total_energy_out / total_energy_in is what matters, not any Q related to plasma energy. Since to build a power plant we just care what it consumes in comparison with what it produces. For this particular case even though Qα > 1 you likely can extract just a tiny fraction of that energy stored in plasma, while spending huge amounts of energy to heat it in the first place. 1. https://www.youtube.com/watch?v=LJ4W1g-6JiY https://www.youtube.com/watch?v=LJ4W1g-6JiY or as an article http://backreaction.blogspot.com/2021/10/how-close-is-nuclear-fusion-power.html http://backreaction.blogspot.com/2021/10/how-close-is-nuclea... Edit: I'm a big proponent of nuclear fission and fusion since both are the best (current and future) way of getting carbon neutral energy, which can cover the spikes in the grid and sun/wind-less days. It is just important to be careful with the terminology, which can be used to make research results more optimistic.

ninkendo 5y ago
So their denominator (energy in) is calculated in terms of the work that was usefully done in compressing the plasma, and not the total energy they used to make said work happen? Any idea what multiple of PdV the input power was? (ie. energy used to power the lasers?) I'm curious what their total Q value would be in this experiment...
- leephillips 5y ago
  This type of laser is about 1% efficient (someone will correct me if I’m out of date on this, but it’s not likely to be better than 10%). Laser fusion really has nothing to do with energy production.
jahnu 5y ago
That's a great video. Her videos often offer a really refreshing sceptical balance to the dominant overly optimistic and downright incorrect pop-sci stuff out there.
ncmncm 5y ago
And, even if they got the actual Q up by two orders of magnitude, inertial D-D fusion can never be practical, because you can't fuse enough. And, even if you confined it magnetically, it costs so much to extract D-D energy that it can never compete even with fission. So it is really a dead end.
dwwoelfel 5y ago
At the end of the video you linked, she accuses the author of The Star Builders of "only briefly mention[ing] the total energy gain and never giv[ing] a number". I had just started the book when I watched her video, and I counted four separate times where he did mention total energy gain. In one chapter (pg. 142 in my kindle edition), he quotes from a source who lays out the distinction she claims people in fusion research want you to be confused about: Like First Light Fusion, Tokamak Energy is much more interested in power production than energy breakeven. "Achieving a of one is a scientific goal," Jonathan Carling continues, "but it's nowhere near enough to produce commercial energy, which requires a Q [in the region] of tens." As mentioned previously, Q is the ratio of fusion power out to heating power in. His strong view is that unless other star builders have a credible plan to get to factors of twenty or thirty more power out than they put in, then they're in the science game and not the fusion energy game. This video by the Improbable Matter channel has a good response to Dr. Hossenfelder's general remarks: https://www.youtube.com/watch?v=KtqC8W0_Ups https://www.youtube.com/watch?v=KtqC8W0_Ups
- ninkendo 5y ago
  I don't think your quote from the book conflicts with Dr. Hossenfelder's criticisms at all. The quote vaguely says "Q = 1 is a scientific goal", then describes Qplasma (and calls it Q): "Q is the ratio of fusion power out to heating power in" (that sounds like Qplasma to me.) The source in the book is basically saying "Q[plasma] needs to be twenty or thirty times higher than it is to get more _power_ out than you put in", but there's already a term for that: Qtotal. Hossenfelder's claim was that the book never mentions Qtotal and continues the misleading technique of using Qplasma as if it's an indicator of power production (and saying it needs to be 20-30x), rather than using a much more clear term Qtotal to describe "total" energy out vs energy in. The response video you linked is even worse: They "correct" Dr. Hossenfelder by showing papers that spout Qplasma numbers as just "Q" and talk about how ITER achieves a Q=10. But that's not in contradiction at all with Dr. Hossenfelder; her qualm is how misleading it is to talk about "Q > 1" as if it's producing useful energy when you actually mean "Qplasma > 1" (which does not produce useful energy.) The response video then goes on to talk about how useful Qplasma is, but that doesn't matter to Dr. Hossenfelder's point, which is that it is unethical to go around touting "We're going to get 10x the energy out that we put in" when you're just referring to Qplasma=10. That's all her video said, and the response is attacking a straw man.
leephillips 5y ago
Yes, that should be required reading/viewing for anyone inclined to take a press release about fusion from a national lab at face value—especially anything related to laser fusion.
ivalm 5y ago
> one can think about it as an explosion rather that intuitive burning (somewhat continuous process). Inertial fusion is an explosion. This milestone is about making these (laser induced) explosions energy positive.
willis936 5y ago
I simply do not have the time or energy to dispel all of the myths Sabine's words have conjured in the past half year all over again. Her argument is convincing laypeople that scientists and engineers who devote their lives to difficult, underpaying work are trying to cheat the public. As someone who has worked in fusion I can tell you there is exactly one reason why people work in fusion and it is to secure humanity's future. No level of cynicism from outsiders will change that fact, only make their lives more difficult. The best I can do for now is point back to prior points at the cracks in the story. https://news.ycombinator.com/item?id=28730707 https://news.ycombinator.com/item?id=28730707 https://news.ycombinator.com/item?id=28736859 https://news.ycombinator.com/item?id=28736859
- lisper 5y ago
  Noble motives are neither necessary nor sufficient to achieve success. The laws of physics neither know nor care how altruistic and self-sacrificing fusion researchers are. If it doesn't work, it doesn't work.
  - willis936 5y ago
    You're absolutely right. And fusion does work. These issues are entirely human.
    - lisper 5y ago
      > fusion does work Right. That's why we have such a thriving fusion power industry.
      - AitchEmArsey 5y ago
        If you broaden the scope of the economy beyond about 1AU, we absolutely do have a thriving fusion power industry.
      - oivey 5y ago
        I think the point he is making is that profitable fusion-based electricity generation isn’t a physics problem; it is an engineering problem. Engineering requires dealing with people in addition to physics.
rndphs 5y ago
The way I understand it, is that with Q>1 in a confined plasma you no longer need external heating and can just let the fusion heat power the plasma. I.e. you "ignite" it and it burns within confinement (self-sustaining). Whereas if Q<1 you need to continuously provide heating, and the efficiency of that heating is probably quite low so the "total" Q appears lower. Basically, once you have ignition + confinement, Q no longer matters as you no longer have to heat the plasma to sustain it. Correct me if I'm wrong.
- JumpCrisscross 5y ago
  > once you have ignition + confinement, Q no longer matters as you no longer have to heat the plasma to sustain it Assuming immutable containment and continuous fusion. In reality, combinations of heat dissipation, cycling (to permit material replacement and/or cooling) and even powering the computers and magnets subtracts from the theoretical power output. In indirect-drive inertial confinement, the NIF drops a Hohlraum containing a fuel pellet and then does things to cause it to fuse. That's the burn. The pellet then falls, a new one is released, and the lasers pulse anew. The energy from the first burn may provide power for the second pulse, but in between is a lot of ground to be lost and thus purchase for Q.
rapht 5y ago
Whatever symbols are used and implied meaning they have (or not), as a layperson I found that the article was very clear that they had not reached any total energy gain (they write something like 0.17 MJ out for 1.9 MJ in).
BlueTemplar 5y ago
Wow, is this weird ! Just a couple hours ago, I've learned about this unfortunate (at best) terminology (as I fell for it too, though at least I knew that ITER wasn't ever supposed to produce electricity), straight from the website of the journalist that stumbled upon the issue (why no link from this blogpost to the original source ?), and was annoyed to see that it didn't seem to having been discussed in ITER discussions here... http://news.newenergytimes.net/2017/10/06/the-iter-power-amplification-myth/ http://news.newenergytimes.net/2017/10/06/the-iter-power-amp...
ChuckMcM 5y ago
Technically the NIF was funded to study nuclear explosions rather than just fusion so nominally so this definition is consistent with their mission. To the extent that one can create fusion events in this way helps all fusion research is also good.
yk 5y ago
The video should be entirely neglected. So yes, you can define your own variables, and in particular what you call Q_total would be important for a power plant. But nobody claims that current fusion experiments are power plants, and as a matter of fact they are not power plants. The Q_total variable is entirely meaningless when talking about them!

by nuccy 5y ago

ninkendo 5y ago

So their denominator (energy in) is calculated in terms of the work that was usefully done in compressing the plasma, and not the total energy they used to make said work happen? Any idea what multiple of PdV the input power was? (ie. energy used to power the lasers?) I'm curious what their total Q value would be in this experiment...

leephillips 5y ago
This type of laser is about 1% efficient (someone will correct me if I’m out of date on this, but it’s not likely to be better than 10%). Laser fusion really has nothing to do with energy production.

jahnu 5y ago

That's a great video. Her videos often offer a really refreshing sceptical balance to the dominant overly optimistic and downright incorrect pop-sci stuff out there.

ncmncm 5y ago

And, even if they got the actual Q up by two orders of magnitude, inertial D-D fusion can never be practical, because you can't fuse enough. And, even if you confined it magnetically, it costs so much to extract D-D energy that it can never compete even with fission. So it is really a dead end.

dwwoelfel 5y ago

At the end of the video you linked, she accuses the author of The Star Builders of "only briefly mention[ing] the total energy gain and never giv[ing] a number". I had just started the book when I watched her video, and I counted four separate times where he did mention total energy gain. In one chapter (pg. 142 in my kindle edition), he quotes from a source who lays out the distinction she claims people in fusion research want you to be confused about: Like First Light Fusion, Tokamak Energy is much more interested in power production than energy breakeven. "Achieving a of one is a scientific goal," Jonathan Carling continues, "but it's nowhere near enough to produce commercial energy, which requires a Q [in the region] of tens." As mentioned previously, Q is the ratio of fusion power out to heating power in. His strong view is that unless other star builders have a credible plan to get to factors of twenty or thirty more power out than they put in, then they're in the science game and not the fusion energy game. This video by the Improbable Matter channel has a good response to Dr. Hossenfelder's general remarks: https://www.youtube.com/watch?v=KtqC8W0_Ups https://www.youtube.com/watch?v=KtqC8W0_Ups

ninkendo 5y ago
I don't think your quote from the book conflicts with Dr. Hossenfelder's criticisms at all. The quote vaguely says "Q = 1 is a scientific goal", then describes Qplasma (and calls it Q): "Q is the ratio of fusion power out to heating power in" (that sounds like Qplasma to me.) The source in the book is basically saying "Q[plasma] needs to be twenty or thirty times higher than it is to get more _power_ out than you put in", but there's already a term for that: Qtotal. Hossenfelder's claim was that the book never mentions Qtotal and continues the misleading technique of using Qplasma as if it's an indicator of power production (and saying it needs to be 20-30x), rather than using a much more clear term Qtotal to describe "total" energy out vs energy in. The response video you linked is even worse: They "correct" Dr. Hossenfelder by showing papers that spout Qplasma numbers as just "Q" and talk about how ITER achieves a Q=10. But that's not in contradiction at all with Dr. Hossenfelder; her qualm is how misleading it is to talk about "Q > 1" as if it's producing useful energy when you actually mean "Qplasma > 1" (which does not produce useful energy.) The response video then goes on to talk about how useful Qplasma is, but that doesn't matter to Dr. Hossenfelder's point, which is that it is unethical to go around touting "We're going to get 10x the energy out that we put in" when you're just referring to Qplasma=10. That's all her video said, and the response is attacking a straw man.

leephillips 5y ago

Yes, that should be required reading/viewing for anyone inclined to take a press release about fusion from a national lab at face value—especially anything related to laser fusion.

ivalm 5y ago

> one can think about it as an explosion rather that intuitive burning (somewhat continuous process). Inertial fusion is an explosion. This milestone is about making these (laser induced) explosions energy positive.

willis936 5y ago

I simply do not have the time or energy to dispel all of the myths Sabine's words have conjured in the past half year all over again. Her argument is convincing laypeople that scientists and engineers who devote their lives to difficult, underpaying work are trying to cheat the public. As someone who has worked in fusion I can tell you there is exactly one reason why people work in fusion and it is to secure humanity's future. No level of cynicism from outsiders will change that fact, only make their lives more difficult. The best I can do for now is point back to prior points at the cracks in the story. https://news.ycombinator.com/item?id=28730707 https://news.ycombinator.com/item?id=28730707 https://news.ycombinator.com/item?id=28736859 https://news.ycombinator.com/item?id=28736859

lisper 5y ago
Noble motives are neither necessary nor sufficient to achieve success. The laws of physics neither know nor care how altruistic and self-sacrificing fusion researchers are. If it doesn't work, it doesn't work.
- willis936 5y ago
  You're absolutely right. And fusion does work. These issues are entirely human.
  - lisper 5y ago
    > fusion does work Right. That's why we have such a thriving fusion power industry.
    - AitchEmArsey 5y ago
      If you broaden the scope of the economy beyond about 1AU, we absolutely do have a thriving fusion power industry.
    - oivey 5y ago
      I think the point he is making is that profitable fusion-based electricity generation isn’t a physics problem; it is an engineering problem. Engineering requires dealing with people in addition to physics.

rndphs 5y ago

The way I understand it, is that with Q>1 in a confined plasma you no longer need external heating and can just let the fusion heat power the plasma. I.e. you "ignite" it and it burns within confinement (self-sustaining). Whereas if Q<1 you need to continuously provide heating, and the efficiency of that heating is probably quite low so the "total" Q appears lower. Basically, once you have ignition + confinement, Q no longer matters as you no longer have to heat the plasma to sustain it. Correct me if I'm wrong.

JumpCrisscross 5y ago
> once you have ignition + confinement, Q no longer matters as you no longer have to heat the plasma to sustain it Assuming immutable containment and continuous fusion. In reality, combinations of heat dissipation, cycling (to permit material replacement and/or cooling) and even powering the computers and magnets subtracts from the theoretical power output. In indirect-drive inertial confinement, the NIF drops a Hohlraum containing a fuel pellet and then does things to cause it to fuse. That's the burn. The pellet then falls, a new one is released, and the lasers pulse anew. The energy from the first burn may provide power for the second pulse, but in between is a lot of ground to be lost and thus purchase for Q.

rapht 5y ago

Whatever symbols are used and implied meaning they have (or not), as a layperson I found that the article was very clear that they had not reached any total energy gain (they write something like 0.17 MJ out for 1.9 MJ in).

BlueTemplar 5y ago

Wow, is this weird ! Just a couple hours ago, I've learned about this unfortunate (at best) terminology (as I fell for it too, though at least I knew that ITER wasn't ever supposed to produce electricity), straight from the website of the journalist that stumbled upon the issue (why no link from this blogpost to the original source ?), and was annoyed to see that it didn't seem to having been discussed in ITER discussions here... http://news.newenergytimes.net/2017/10/06/the-iter-power-amplification-myth/ http://news.newenergytimes.net/2017/10/06/the-iter-power-amp...

ChuckMcM 5y ago

Technically the NIF was funded to study nuclear explosions rather than just fusion so nominally so this definition is consistent with their mission. To the extent that one can create fusion events in this way helps all fusion research is also good.

yk 5y ago

The video should be entirely neglected. So yes, you can define your own variables, and in particular what you call Q_total would be important for a power plant. But nobody claims that current fusion experiments are power plants, and as a matter of fact they are not power plants. The Q_total variable is entirely meaningless when talking about them!