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I'm always suspicious of "breakthrough" announcements when it comes to fusion, especially ones that originate from a college's PR office. Can someone put this i

by matt2000 11y ago

I'm always suspicious of "breakthrough" announcements when it comes to fusion, especially ones that originate from a college's PR office. Can someone put this in context for us? Is it a big deal?

Retric 11y ago
"Breakthrough" as in progress, not solution. It's a meaningful and useful step forward, but it does not directly suggest any design changes.
- cmpb 11y ago
  It could prompt a change to the design of the model and/or modeling software/hardware, no?
  - Retric 11y ago
    In terms of Modeling software, it's really expensive. So, it can help validate a design, but it's not the kind of thing you want running after every incremental change.
ogrisel 11y ago
It's a theoretical breakthrough that explains an unexpectedly bad behavior of current designs that was not understood so far: a discrepancy between theory and experimental observations. Now that the model is fine enough to explain the turbulences observed in the experiments one might hope that this will help suggest design changes to better deal with the turbulences. However the MIT article does not suggest any practical design modification yet.
- semi-extrinsic 11y ago
  It is a hard thing to write the code for and then run a simulation of coupled plasma turbulence taking 15 million CPU-hours to explain a phenomenon. But it is another thing entirely to take such a huge simulation and try to use many of them to do tokamak design optimization.
  - marktangotango 11y ago
    Indeed, I found this quote from the original article relevant: >> Now, researchers at General Atomics are taking these new results and using them to develop a simplified, streamlined simulation that could be run on an ordinary laptop computer
    - ogrisel 11y ago
      Maybe this could be done with machine learning to learn an approximate function to predict the outcome of the paired simulation from the outcome of the isolated simulations.
  - S_A_P 11y ago
    I would be curious to know the process for even modeling this sort of thing. How do they know they got it right? How accurately does this model existing experiments? Im also wondering if they model to a result vs modeling to what should actually be happening. Would anyone learned on this subject please chime in? I've always wondered how modeling these types of complex systems works.
    - tfgg 11y ago
      I think the answer is "with great difficulty". When you're developing something like this, you might have an issue with: - Experiment - Model - Approximation to the model - Numerics - Code (- Compiler & hardware) So, your answer might not match experiment. Maybe the experiment is wrong. Maybe it's an expected effect due to an approximation you used. Maybe your integration grid isn't sufficiently converged. You just have to systematically eliminate these, often by comparing to more expensive but verified simulations, or analytic solutions on simplified models.
    - evanb 11y ago
      I don't do plasma physics but other sorts of HPC numerical physics. The answer is a myriad of ways: Check small numerical cases on an already-validated code. Check problems for which you have an analytic solution (in this case, maybe many laminar flow scenarios). Check problems where the 'weird part' (ie the turbulence in this case) is limited to one small part of the simulation. Compare only moderately complicated simulations to experiments that are already entirely understood.
- brgewut 11y ago
  So the current designs don't work? Sounds more like a step back not a "breakthrough"
  - Bjartr 11y ago
    Discovering your believed correct model is wrong is a scientific breakthrough, as is discovering how to fix it.
    - brgewut 11y ago
      Ok, I thought "breaktrough" brings you closer to something. Eg. saying that "switch to Heliocentric worldview was a major breakthrough for Geocentric theory" sounds really weird to me.
      - nevir 11y ago
        Better understanding does bring you closer to making something tangible happen. The heliocentric theory was a breakthrough for a variety of technologies. We certainly would have found going into space much more difficult if we still followed the geocentric theory.
      - Scarblac 11y ago
        The step is that they figured out _why_ reality wasn't as good as the model. Another way to put it is that they improved the model. That _does_ bring us closer to improving actual reactors.
      - daveguy 11y ago
        The breakthrough would be more like saying, "the switch to heliocentric worldview was a major breakthrough for solar system modeling." 1) The reactors have been failing to generate sustained plasma due to specific failures. 2) The simulation models of the reactors did not correctly predict those failures. 3) The new model correctly predicts those failures. 4) Now you can iterate designs using the model with the expectation that these particular failures can be identified before building a full reactor. 5) Breakthrough.
Animats 11y ago
Yes, this is progress in understanding plasma behavior. No, it's not Commercial Fusion Real Soon Now. MIT did not overhype this. The MIT news office used the title "New finding may explain heat loss in fusion reactors".[1] The site from which this was taken added the clickbait title. [1] http://news.mit.edu/2016/heat-loss-fusion-reactors-0121 http://news.mit.edu/2016/heat-loss-fusion-reactors-0121
drjesusphd 11y ago
As you should be. There is a lot of press out there about "get rich quick" schemes for fusion which have little to no foundation in plasma physics. This is an example of real progress being made in magnetic confinement. It's not promising a burning reactor in less 10 years (ahem...). All told, the mainstream scientific community has been very responsible lately in what claims they make about fusion. It's the contractors and startups who think career scientists don't know what they're doing that are over-hyping their pet schemes. I honestly wish them the best of luck, but what I resent is the credibility gap that fusion scientists work under due to their broken promises.
lutusp 11y ago
> Is it a big deal? It seems to be a step toward making our models agree with actual observations, which in general is a very good thing. As to whether it's a big deal WRT actual fusion, that will have to wait until someone thinks of a way to apply this result to present tokamak designs.
Obi_Juan_Kenobi 11y ago
This makes a major design challenge tractable. Now modelling can be used to predict plasma behavior, whereas before it would not reflect experimental observations. If you can simulate a design hypothesis instead of having to build an actual reactor, you can make a lot more progress. Understanding the phenomena should also inform the design process.

I'm always suspicious of "breakthrough" announcements when it comes to fusion, especially ones that originate from a college's PR office. Can someone put this in context for us? Is it a big deal?

Retric 11y ago

"Breakthrough" as in progress, not solution. It's a meaningful and useful step forward, but it does not directly suggest any design changes.

cmpb 11y ago
It could prompt a change to the design of the model and/or modeling software/hardware, no?
- Retric 11y ago
  In terms of Modeling software, it's really expensive. So, it can help validate a design, but it's not the kind of thing you want running after every incremental change.

ogrisel 11y ago

It's a theoretical breakthrough that explains an unexpectedly bad behavior of current designs that was not understood so far: a discrepancy between theory and experimental observations. Now that the model is fine enough to explain the turbulences observed in the experiments one might hope that this will help suggest design changes to better deal with the turbulences. However the MIT article does not suggest any practical design modification yet.

semi-extrinsic 11y ago
It is a hard thing to write the code for and then run a simulation of coupled plasma turbulence taking 15 million CPU-hours to explain a phenomenon. But it is another thing entirely to take such a huge simulation and try to use many of them to do tokamak design optimization.
- marktangotango 11y ago
  Indeed, I found this quote from the original article relevant: >> Now, researchers at General Atomics are taking these new results and using them to develop a simplified, streamlined simulation that could be run on an ordinary laptop computer
  - ogrisel 11y ago
    Maybe this could be done with machine learning to learn an approximate function to predict the outcome of the paired simulation from the outcome of the isolated simulations.
- S_A_P 11y ago
  I would be curious to know the process for even modeling this sort of thing. How do they know they got it right? How accurately does this model existing experiments? Im also wondering if they model to a result vs modeling to what should actually be happening. Would anyone learned on this subject please chime in? I've always wondered how modeling these types of complex systems works.
  - tfgg 11y ago
    I think the answer is "with great difficulty". When you're developing something like this, you might have an issue with: - Experiment - Model - Approximation to the model - Numerics - Code (- Compiler & hardware) So, your answer might not match experiment. Maybe the experiment is wrong. Maybe it's an expected effect due to an approximation you used. Maybe your integration grid isn't sufficiently converged. You just have to systematically eliminate these, often by comparing to more expensive but verified simulations, or analytic solutions on simplified models.
  - evanb 11y ago
    I don't do plasma physics but other sorts of HPC numerical physics. The answer is a myriad of ways: Check small numerical cases on an already-validated code. Check problems for which you have an analytic solution (in this case, maybe many laminar flow scenarios). Check problems where the 'weird part' (ie the turbulence in this case) is limited to one small part of the simulation. Compare only moderately complicated simulations to experiments that are already entirely understood.
brgewut 11y ago
So the current designs don't work? Sounds more like a step back not a "breakthrough"
- Bjartr 11y ago
  Discovering your believed correct model is wrong is a scientific breakthrough, as is discovering how to fix it.
  - brgewut 11y ago
    Ok, I thought "breaktrough" brings you closer to something. Eg. saying that "switch to Heliocentric worldview was a major breakthrough for Geocentric theory" sounds really weird to me.
    - nevir 11y ago
      Better understanding does bring you closer to making something tangible happen. The heliocentric theory was a breakthrough for a variety of technologies. We certainly would have found going into space much more difficult if we still followed the geocentric theory.
    - Scarblac 11y ago
      The step is that they figured out _why_ reality wasn't as good as the model. Another way to put it is that they improved the model. That _does_ bring us closer to improving actual reactors.
    - daveguy 11y ago
      The breakthrough would be more like saying, "the switch to heliocentric worldview was a major breakthrough for solar system modeling." 1) The reactors have been failing to generate sustained plasma due to specific failures. 2) The simulation models of the reactors did not correctly predict those failures. 3) The new model correctly predicts those failures. 4) Now you can iterate designs using the model with the expectation that these particular failures can be identified before building a full reactor. 5) Breakthrough.

Animats 11y ago

Yes, this is progress in understanding plasma behavior. No, it's not Commercial Fusion Real Soon Now. MIT did not overhype this. The MIT news office used the title "New finding may explain heat loss in fusion reactors".[1] The site from which this was taken added the clickbait title. [1] http://news.mit.edu/2016/heat-loss-fusion-reactors-0121 http://news.mit.edu/2016/heat-loss-fusion-reactors-0121

drjesusphd 11y ago

As you should be. There is a lot of press out there about "get rich quick" schemes for fusion which have little to no foundation in plasma physics. This is an example of real progress being made in magnetic confinement. It's not promising a burning reactor in less 10 years (ahem...). All told, the mainstream scientific community has been very responsible lately in what claims they make about fusion. It's the contractors and startups who think career scientists don't know what they're doing that are over-hyping their pet schemes. I honestly wish them the best of luck, but what I resent is the credibility gap that fusion scientists work under due to their broken promises.

lutusp 11y ago

> Is it a big deal? It seems to be a step toward making our models agree with actual observations, which in general is a very good thing. As to whether it's a big deal WRT actual fusion, that will have to wait until someone thinks of a way to apply this result to present tokamak designs.

Obi_Juan_Kenobi 11y ago

This makes a major design challenge tractable. Now modelling can be used to predict plasma behavior, whereas before it would not reflect experimental observations. If you can simulate a design hypothesis instead of having to build an actual reactor, you can make a lot more progress. Understanding the phenomena should also inform the design process.