Nuclear Fusion's New Idea: An Off-the-Shelf Stellarator

(spectrum.ieee.org)

65 points | by mfiguiere 9 hours ago ago

20 comments

  • rgmerk 5 hours ago

    Cool.

    But even if you have a working stellarator that's a very long way from an economically viable energy source. You've still got to a) figure out how to cheaply convert the released energy into electricity (and the baseline way of doing that in D-T fusion is...a steam turbine), and b) figure out materials that can survive the radiation bombardment for a sufficiently long time.

    In sunny places (and I fully acknowledge that's not all of the world) it's still going to be hard to beat sticking bits of special glass out in a field and connecting wires to it.

    But we should sure as heck keep tinkering away at it!

    • tomxor 4 hours ago

      I don't think the point of this project is to be closer to economic viability, but to demonstrate an approach that would lead to faster economic viability due to allowing faster iteration and evaluation of small scale experimental designs.

      In HN terms they are demonstrating a significantly faster REPL by keeping the project small and minimising use of esoteric or highly bespoke components.

      It's the closest you can get to building your own stellarator by walking into radioshack. I think it's a pretty cool idea.

      • rgmerk 2 hours ago

        Yep, sure. And that's great.

    • dexwiz 4 hours ago

      Newer solar panels don’t need full sun to function. It’s economically viable to place them further north and in cloudier climates now. So the area where these are alternatives are viable may be shrinking faster than you would expect.

      • cm2187 35 minutes ago

        Well as long as you have vast amount of storage capacity + overprovision, or an alternative source of on-demand electricity, the cost of which I never see included when comparing to on-demand energy sources like nuclear of fossil fuels.

      • rgmerk 2 hours ago

        Indeed, though in colder climates you do have the problem that peak electricity demand is precisely when you get minimum solar production.

        But in sunnier, warmer parts of the world (which notably includes India, Pakistan, Bangladesh, Indonesia, Nigeria, Egypt, Ethiopia, Iran, Mexico, and Brazil, amongst others), over the next few decades it's hard to see anything much competing against solar and batteries for the bulk of energy usage.

  • timoth3y 2 hours ago

    I'm having trouble understanding what's actually been accomplished here. The article provides a good overview of Tokamak vs Stellarator, but seems to jump back and forth between proclaiming this as an innovative breakthrough and saying it's just a framework to test ideas.

    > In terms of its ability to confine particles, Muse is two orders of magnitude better than any stellarator previously built

    Is it? It doesn't seem as if they have reached first plasma or have plans to do so anytime soon. Using electromagnets to not only confine but also to control the the plasma is a big selling point of the stellarator design, and they don't seem to address this.

    This seems really cool, and I love the idea of lower-cost fusion. (Or even just functional fusion.) There are about a dozen companies making real progress in fusion, but I can't quite figure out what this team has actually accomplished.

    What am I missing?

  • jayyhu 3 hours ago

    The actual paper describing the construction of the MUSE Stellarator: https://www.cambridge.org/core/journals/journal-of-plasma-ph...

  • King-Aaron 5 hours ago

    I admittedly don't know much about fusion reactors, but I do love that the thing which you create a star within is called a "Stellarator".

  • BenFranklin100 4 hours ago

    “PPPL researchers say their simpler machine demonstrates a way to build stellarators far more cheaply and quickly, allowing researchers to easily test new concepts for future fusion power plants.”

    This quote reminded of the SpaceX’s approach to engineering and why they have leapfrogged past Boeing. Instead of spending 10-20 years and billions into a single design, SpaceX iterates.

  • credit_guy 5 hours ago

    People don't understand the fundamental problem of fusion. It's a problem of energy loss. Of enormous energy losses.

    Roughly speaking energy can be mechanical, for particles or radiative, for photons. The first one is proportional to the temperature (the famous NRT) and the second is proportional to the fourth power of the temperature. The constant of proportionality is very small, and at regular temperatures we generally don't think of it that much. But at millions of degrees Kelvin, it starts to dominate all considerations.

    The heat always moves form hot to cold. In the case of particles the heat flow is proportional to the difference in temperature, and in the case of radiation with the difference in temperature to the power 4. But heat also travels from particles to photons and vice-versa. It doesn't matter how.

    The problem with fusion is now this. Suppose that you have a super-duper device, let's call it brompillator. It brings an amount of deuterium-tritium mix at the required temperature, let's say 10 million Kelvin. Now that volume of plasma is surrounded by cold stuff. You can imagine that you have some mirrors, or magnetic fields, or some magic stuff, but the cold hard stuff is that that plasma will want to radiate to the exterior and the flow of heat would be proportional to the surface area times the fourth power of the difference in temperature. Since for all practical purposes the outer temperature is zero, we are talking about the fourth power of 10 million Kelvin. Now that constant of porportionality is very small, it is called the Stefan-Boltzman constant and has a value of about 10^7 W m^-2 K^-4. Let's say the surface area is 1 square meter. So the heat loss happens at a rate of 10^-7 times (10^7)^4 = 10^21 Watts. That is 10^12 GigaWatts. One GW is the output of a decent sized nuclear power plant.

    Of course, you can try to shield that plasma, but that shield has to be 99.99999....9% effective, where the number of 9s needs to be about 15 or so.

    That is the immensity of the challenge that nobody is willing to tell you about.

    How was this overcome in the case of the thermonuclear bomb? People imagine that once you have a fission bomb, you just put some deuterium-tritium mix next to it, and voila, you have a fusion bomb. No. The world's greatest minds have worked at this issue for about 5 years. The solution was something like this: if you first compress significantly the volume of fusion fuel, then the heat losses are much smaller (remember they are proportional to the area, and that's proportional to the square of the radius). They will still be tremendous, but you don't even aim to keep the reaction going for a long time. The duration of the fusion reaction in a thermonuclear bomb is still classified information, but public sources put it at the order of 1 microsecond. The heat losses are still tremendous, but for a short moment the heat gains from the fusion reaction are even greater, so ignition is achieved.

    In the NIF experiment that achieved more than breakeven 2 years ago, the fusion lasted less than 10 nanoseconds [1].

    If someone thinks the brompillator will achieve fusion and that will run for years, or even hours, or seconds, they don't understand the fundamental problem. Unfortunately, nobody is willing to ask hard questions about this, not even Sabine Hossenfelder.

    [1] https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.132.065...

    • minetest2048 an hour ago

      I don't disagree with this statement, fusion researchers do care about energy loss when they're evaluating fusion reactor feasibility. They talk more about neutron loss, bremsstrahlung radiation and synchrotron radiation instead of blackbody radiation. A paper on this: https://arxiv.org/pdf/2104.06251

      So I did some searching, and found this stack exchange asking this question: https://physics.stackexchange.com/questions/415028/how-do-fu... . They argued that because fusion reactor plasma is optically thin, it doesn't radiate following blackbody radiation law. This textbook also say that: https://www.cambridge.org/core/books/abs/physics-of-plasmas/...

      I tried to search more about plasma energy losses, and it becomes extremely complicated with insane amount of equations. One thing that I can get is that you can't model fusion reactor plasmas as a blackbody radiator because plasma is that complicated. If plasma is simpler then we should either have fusion already or we have given up on fusion research a long time ago

    • liftm an hour ago

      I'm a physics layman, and I'm having some trouble with uniting the content of your comment with the fact that existing magnetic confinement experiments have reported maintaining a plasma at the right temperature for longer times (not with fusion, but with microwave heating, and with the power of those heaters in the 10MW range).

      Have I understood the consequences of those reports wrong? Does the heat loss you talk about only occur with fusion? (And if so, is it even a problem if the conditions for fusion to occur can be created by external heating this "easily"?)

      • adastra22 14 minutes ago

        In order to protect astronauts from decompression, the hull of a spacecraft has to be insanely good at stopping gas particles. Not 99.5% good, but like 99.9999999…% with 20 zeros! That’s very good.

        But a thin metal sheet has no trouble doing this, as demonstrated by the Apollo lunar lander.

        Some things are just not as hard as they sound. Magnetic confinement works very well. It easily achieves the necessary 9’s.

        It’s just hard to keep it stable at millions of degrees, but that’s a different problem.

        • matt123456789 8 minutes ago

          Wait til you guys hear about DNA transcription error rates!

    • twic 4 hours ago

      > People don't understand the fundamental problem of fusion. It's a problem of energy loss. Of enormous energy losses.

      I'm not sure that's even true, because if you manage to crack that, you still have the problem that your sustainable reaction is pumping out most of its energy in the form of very fast neutrons, which are (a) very hard to harvest energy from and (b) extremely bad for people and materials if you don't. You could have a self-sustaining reaction that you can't actually use!

      • chasil 4 hours ago

        Aneutronic fusion has been previously mentioned, specifically HB11.

        https://en.m.wikipedia.org/wiki/Aneutronic_fusion

      • pfdietz 2 hours ago

        Also, the fusion reactors will inevitably have poor volumetric power density, due to limits on power/area through the first wall and the square-cube law.

        Engineering studies of stellarators found they tend to be larger and have worse economics than tokamaks.

    • evnp 2 hours ago

      Just wanted to say thank you for this comment, fascinating and perfect example of the beauty of HN. Relatively fresh off The Making of the Atomic Bomb and while fusion was not at all a focus, this (incomplete) impression is exactly what I came away with.

      Is there any chance you'd recommend any books related to these topics? The walk through decades of revelations in physics was the most enjoyable aspect of that book, I'd love to continue building on that story.

    • fallingknife an hour ago

      Inertial confinement fusion like the NIF is not intended to run continuously, so the 2ns duration is irrelevant. The surface area for the calculation is not the surface area of the machine, but the surface area of the volume in which the fusion is occurring which could be very much smaller than that.

      The heat loss is practically limited by the mass of hydrogen fusing in the machine. To have a continuous heat flux of 10^21 watts you would need to fuse ~4*10^5 kg of hydrogen every second. Which clearly these machines are not intended to do.