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posted by janrinok on Monday November 21, @01:54PM   Printer-friendly
from the burn-baby-burn dept.

There's a change in behavior when the plasma starts burning, and nobody knows why:

[...] Now, researchers have analyzed the properties of the plasma as it experiences these high-energy states. And to their surprise, they found that burning plasmas appear to behave differently from those that have experienced ignition. At the moment, there's no obvious explanation for the difference.

In the experiments, the material being used for fusion is a mix of tritium and deuterium, two heavier isotopes of hydrogen. These combine to produce a helium atom, leaving a spare neutron that's emitted; the energy of the fusion reaction is released in the form of a gamma ray.

The fusion process is triggered by a short, extremely intense burst of laser light that targets a small metallic cylinder. The metal emits intense X-rays, which vaporize the surface of a nearby pellet, creating an intense wave of heat and pressure on the pellet's interior, where the deuterium and tritium reside. These form a very high-energy plasma, setting the conditions for fusion.

If everything goes well, the energy imparted ignites the plasma, meaning that no additional energy is needed for the fusion reactions to continue for the tiny fraction of a second that passes before the whole thing blows apart. At even higher energies, the plasma reaches a state called burning, where the helium atoms that are forming carry so much energy that they can ignite the nearby plasma. This is considered critical because it means the rest of the energy (in the form of neutrons and gamma rays) can potentially be harvested to produce useful power.

While we have detailed models of the physics that goes on under these extreme conditions, we need to compare those models to what's going on inside the plasma. Unfortunately, given that both the plasma and the materials that formerly surrounded it are in the process of exploding, that's a significant challenge. To get a picture of what might be going on, researchers have turned to one of the products of the fusion reaction: the neutrons it emits, which can pass through the wreckage and be picked up by nearby detectors.

Hartouni, E.P., Moore, A.S., Crilly, A.J. et al. Evidence for suprathermal ion distribution in burning plasmas. Nat. Phys. (2022). DOI: 10.1038/s41567-022-01809-3 (About DOIs).


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  • (Score: 5, Insightful) by looorg on Monday November 21, @03:32PM (8 children)

    by looorg (578) on Monday November 21, @03:32PM (#1280814)

    Once the plasma switches over to burning, however, things no longer match. It's like the neutron data finds a completely different curve and follows along that instead.

    But is the outcome better or worse? It seems a bit unclear but from what I can gather we are getting more or higher results then predicted. So outcome wise it is better then? But still bad since we failed to predict it. Clearly we didn't describe the reaction properly before.

    But if it's following a new curve then at least it's on a curve so it should not be that hard to figure out this new curve and follow and make changes to the prediction. It's just a matter of experimentation then to figure out what triggers this new curve and when or what. Science!

    That said they should be a lot more excited. After all unexpected scientific results makes for so much more interesting papers. Unless it is you that borked it and it's all down to some combination of faulty math and/or experimentation, ie all your fault.

    • (Score: 4, Insightful) by Revek on Monday November 21, @04:34PM (6 children)

      by Revek (5022) on Monday November 21, @04:34PM (#1280829)

      No kidding, they went out of their way to not reveal if this was a positive or a negative possibility.

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      • (Score: 4, Insightful) by JoeMerchant on Monday November 21, @06:44PM (5 children)

        by JoeMerchant (3937) on Monday November 21, @06:44PM (#1280860)

        "We got a result that's different than expected, but we're not going to say which direction yet because we just don't understand our own results enough" - maybe not enough to know whether it translates to better or worse fusion in the end analysis, yet.

        Or, it's just horrendous reporting and the reporter should receive a ban until they can pass a basic logical communication test. Even if the researchers aren't calling the direction, that should have been somewhere in the first paragraph.

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        • (Score: 2) by looorg on Monday November 21, @07:58PM (3 children)

          by looorg (578) on Monday November 21, @07:58PM (#1280877)

          I guess it's a matter of perspective, usage or the goal. One would think they would be happy if it created more energy then they thought it would, yay more/free energy! Or it's really bad and it risks becoming a fusion bomb, unless that is what you wanted and then once again yay free energy! I just assume you don't like to work with surprise amounts of energy when you are doing fusion experiments. Which I guess is the problem at hand. But if they are doing such things one would at least hope they knew or stated if it was good or bad or if they have not decided yet. Either could work.

          • (Score: 2) by JoeMerchant on Monday November 21, @10:50PM (2 children)

            by JoeMerchant (3937) on Monday November 21, @10:50PM (#1280908)

            As far as I understand, at this stage the problem is plasma containment for a self sustaining reaction. If the energy release is more "bursty" or chaotic than expected I would imagine the containment challenge is greater.

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            • (Score: 2) by HiThere on Friday December 02, @04:57PM (1 child)

              by HiThere (866) on Friday December 02, @04:57PM (#1280944) Journal

              This is the laser fusion system. I don't think they intend to get self-sustaining reactions. What they want (well, what they would want if they were after power rather than research) is lots of predictable energy yielding reactions in a fairly short amount of time. Rather like the pistons in an internal combustion engine.

              But this is a research set-up, so what they really want to do is to be able to predict how things will work before they happen.

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              • (Score: 2) by JoeMerchant on Friday December 02, @05:02PM

                by JoeMerchant (3937) on Friday December 02, @05:02PM (#1280946)

                Yeah, I caught a later news story explaining better: the fusion fuel is encapsulated inside a diamond shell and ignited with a laser pulse. The more powerful the laser pulse, the thicker the diamond shell can be (otherwise it doesn't break through in the clean/predictable manner they are counting on)... but... when they got a super good yield from the experiment, it became unreliable - hard to repeat - and apparently it takes days to weeks between pulse shots.

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        • (Score: 3, Insightful) by RS3 on Monday November 21, @08:29PM

          by RS3 (6367) on Monday November 21, @08:29PM (#1280886)

          Or, it's just horrendous reporting and the reporter should receive a ban until they can pass a basic logical communication test.

          I get where you're coming from, but please be careful with that. As an engineer I bristle when I hear or read someone bashing engineers because something doesn't work correctly. I'm the guy who is always trying to get something _right_, and the boss says "I don't care, ship it!" We live in a messed up world.

          Most building, bridge, etc. failures are due to construction mistakes, shortcuts, misinterpretation, as-built / on-the-fly changes, materials and components that don't actually pass required specifications, IE, problems are not in the original design.

          The world of journalism is fraught with deadlines, which are rarely long enough, and the short rush almost always causes people to compromise.

          Bottom line, for me anyway, is: read with "a grain of salt".

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    • (Score: 2) by RamiK on Monday November 21, @09:51PM

      by RamiK (1813) on Monday November 21, @09:51PM (#1280899)

      But is the outcome better or worse?

      the average neutron energy produced is higher than expected for a deuterium-tritium (D-T) plasma that is in thermal equilibrium...for DT reactions, NIF implosions exceed this relationship once they start to burn and ignite, indicating that the ions have more energy than expected based on the plasma temperature we measure, which led us to the term suprathermal

      ( https://www.llnl.gov/news/llnl-researchers-observe-ions-behave-differently-fusion-reactions [llnl.gov] )

      What it means in practice is that the existing theory is off and all the talks about fusion being just around the corner are bullshit. However, it also means there's more energy to be had so there might actually be some long term utility in all of this after the theorists put together new equations. So, bad short term. Good long term.

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  • (Score: 2) by istartedi on Monday November 21, @08:24PM (3 children)

    by istartedi (123) on Monday November 21, @08:24PM (#1280883) Journal

    It's kind of scary how bad we are at predicting the outcomes of nuclear reactions. This time the result is merely "interesting" but there have been other times where failure to accurately predict the reaction was tragic [wikipedia.org]. Hopefully it doesn't get much worse than that. I'm given to understand we model nuclear bombs using supercomputers now. I like to think that if we plug the preconditions for Castle Bravo in to those models it comes back with the proper yield. Maybe they can take these plasma results and use them to improve those models also. At least *we're* not doing actual bomb tests any more. I'm looking at you, fat-boy.

    • (Score: 2) by takyon on Tuesday November 22, @01:26AM (1 child)

      by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Tuesday November 22, @01:26AM (#1280933) Journal

      Tests are scheduled to resume soon, with a focus on population centers.

      https://www.youtube.com/watch?v=T2I66dHbSRA [youtube.com]
      https://img.youtube.com/vi/T2I66dHbSRA/maxresdefault.jpg [youtube.com]

      Still one of the most beautiful disasters ever known.

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      • (Score: 3, Interesting) by istartedi on Tuesday November 22, @01:50AM

        by istartedi (123) on Tuesday November 22, @01:50AM (#1280938) Journal

        The sound of that plane is almost certainly dubbed in. Actual audio from nuke tests is rare, the only full audio-visual I'm aware of is this one [youtube.com]. Note that the sound when the bomb goes off is obviously an artifact of the filming process--audio was encoded using light on the film. Attempting to make the audio track light-tight under the intense flash of a nuke blast was obviously not a consideration. The result is, IMHO, an appropriately ominous sound even though it's not "real".

    • (Score: 2) by JoeMerchant on Friday December 02, @05:05PM

      by JoeMerchant (3937) on Friday December 02, @05:05PM (#1280947)

      Simulations work well, until they don't. And, each time they don't is a learning opportunity to make the imperfect model a little better next time.

      The devil is in the variables, particularly the uncontrolled ones.

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