5 ms·

And what about non-DT fusion? Helion, funded by Sam Altman, is doing DD/DHe3 fusion. Non-thermal fusion with direct energy conversion. They are attempting net

• pfdietz 4y ago
  That's why I was careful to write "DT". :) If someone held a gun to my head and forced me to invest in a fusion effort, it would be Helion.
• acidburnNSA 4y ago
  Considering how much less likely the non-DT reactions are than DT ones from a nuclear physics perspective at reasonable plasma temperature, I'd say it's an extra long shot. We'd expect the easy reactions to be done first, followed by the much harder ones. Every advanced anything company says net electricity by 2024. I'm not holding my breath. I'd be thrilled to be wrong.
  • pfdietz 4y ago
    If the physics issues were the only ones facing fusion, you'd be making a good argument there. But after the physics comes engineering. Helion's approach is to be more aggressive on the physics in order to greatly ease the grave engineering issues that face DT reactors. I consider these latter issues to be so serious that, overall, I rate Helion as less of a long shot at achieving practical fusion than any of the DT schemes.
    • smaudet 4y ago
      Not sure why you're being down-voted, easy solutions with numerous problems are generally inferior to more elegant solutions with fewer problems, could you enumerate what these issues are between Helion and DT reactors?
      • pfdietz 4y ago
        The problems with DT are low power density due to limits on power/area through the first wall, neutron damage to reactor materials, getting tritium breeding to work, and the need for a large non-nuclear part of the plant (turbine, generator). Helion potentially avoids or ameliorates all of these problems. Unlike with DT, where 80% of the power is in neutrons, a smaller fraction of power is from neutrons here (particularly when there's enough 3He available to be using that too.) The neutrons from DD fusion are much lower energy than from DT fusion, so they produce much less helium in the reactor materials (helium produced there migrates to tiny bubbles where the pressure grows until it rips the material apart.) With Helion, reactor materials have a reasonable shot at lasting the lifetime of the reactor; this is not true for first wall materials in a DT reactor operating at adequate power density. Helion's scheme also directly recovers plasma energy, including fusion energy going to ions, as electrical energy, so it can substantially, perhaps completely, avoid the need for turbines and generators. Helion does not need to breed tritium. All it has to do is capture and store produced tritium from DD reactions (so it can decay to 3He, which would be used), which will be much easier. There is no need for a breeding blanket with lithium, although one could be added if desired. If so, that breeding blanket doesn't have to allow rapid recovery of produced tritium before it decays.
        • joak 4y ago
          Also in Helion machine magnets coils are in aluminum. And because aluminum is (mostly) transparent to neutrons they don't get damaged. This is to be compared with the superconductors of tokamaks. So actually their idea is to put the shield (or the blanket) outside of the reactor, not between the magnets and the plasma. A lot easier to do. There are still many uncertainties, some because they are secretive and others because they have to figure out a solution. They seem pretty confident to reach net electricity in 2024, they might be completely wrong on something and/or underestimating the difficulties. We'll see.
          • pfdietz 4y ago
            I'm not sure about that aluminum argument. Aluminum isn't transparent to neutrons; neutrons will scatter off Al nuclei just fine. Perhaps the metal is more resilient to the resulting damage. The real thing to worry about in neutron irradiation of coils is damage to insulators, not to conductors. Insulators are very sensitive to radiation damage.