5 ms·

The one that gave me most hope from this point of view was the Polywell design. It made some waves a few years ago then got classified and sputtered out, then

The one that gave me most hope from this point of view was the Polywell design. It made some waves a few years ago then got classified and sputtered out, then this happened: https://en.wikipedia.org/wiki/Polywell#%22Final_nail%22 https://en.wikipedia.org/wiki/Polywell#%22Final_nail%22? I'm entirely with you as far as tokamaks go - they're relying on unobtainium for a significant component - but I think other designs are possible, just under-researched.

MauranKilom 6y ago
Are you aware of https://en.wikipedia.org/wiki/Wendelstein_7-X https://en.wikipedia.org/wiki/Wendelstein_7-X? It is well on its way to produce sustained plasma discharges of multiple minutes. The stellarator design has some decisive advantages over Tokamaks.
- pfdietz 6y ago
  It does not avoid the generic problem of DT fusion reactors, which is lousy power density. The magnets are also famously complex and expensive.
  - MauranKilom 6y ago
    That sounds like engineering and scaling challenges, not inherent limitations... I mean, they clearly have the magnets figured out and so far there doesn't seem to have been a lot in the way of unforeseen roadblocks.
    - pfdietz 6y ago
      That sounds like the dismissive attitude a plasma physicist, for whom mere engineering issues are trivial and of lesser importance. But engineering issues are perfectly capable of ruining the prospects for a technology. Fission, for example, faces nothing BUT engineering issues (where cost is considered a part of engineering.) The equivalent of breakeven and ignition was achieved for fission in 1942. DT fusion faces fundamental engineering obstacles, obstacles that are not solvable by tweaking the confinement scheme. Scaling up makes the main problem, power density, worse, not better (see a later comment by me on this issue.)
- m4rtink 6y ago
  I like how the chamber and magnet design looks like something made by Cthulhu in cooperation with Salvador Dali himself. Even just due to that it should work. :)
pfdietz 6y ago
Polywell was 100% BS, I'm afraid. The whole concept of forming a "virtual cathode" made no sense, due to plasma conductivity shorting it out. The group at Sydney who did experiments with similar devices concluded that maintaining the virtual cathode in a reactor-scale Polywell would require a 20 gigawatt electron beam.
- regularfry 6y ago
  That's what the link I gave explains.
  - pfdietz 6y ago
    Thanks.

MauranKilom 6y ago

Are you aware of https://en.wikipedia.org/wiki/Wendelstein_7-X https://en.wikipedia.org/wiki/Wendelstein_7-X? It is well on its way to produce sustained plasma discharges of multiple minutes. The stellarator design has some decisive advantages over Tokamaks.

pfdietz 6y ago
It does not avoid the generic problem of DT fusion reactors, which is lousy power density. The magnets are also famously complex and expensive.
- MauranKilom 6y ago
  That sounds like engineering and scaling challenges, not inherent limitations... I mean, they clearly have the magnets figured out and so far there doesn't seem to have been a lot in the way of unforeseen roadblocks.
  - pfdietz 6y ago
    That sounds like the dismissive attitude a plasma physicist, for whom mere engineering issues are trivial and of lesser importance. But engineering issues are perfectly capable of ruining the prospects for a technology. Fission, for example, faces nothing BUT engineering issues (where cost is considered a part of engineering.) The equivalent of breakeven and ignition was achieved for fission in 1942. DT fusion faces fundamental engineering obstacles, obstacles that are not solvable by tweaking the confinement scheme. Scaling up makes the main problem, power density, worse, not better (see a later comment by me on this issue.)
m4rtink 6y ago
I like how the chamber and magnet design looks like something made by Cthulhu in cooperation with Salvador Dali himself. Even just due to that it should work. :)

pfdietz 6y ago

Polywell was 100% BS, I'm afraid. The whole concept of forming a "virtual cathode" made no sense, due to plasma conductivity shorting it out. The group at Sydney who did experiments with similar devices concluded that maintaining the virtual cathode in a reactor-scale Polywell would require a 20 gigawatt electron beam.

regularfry 6y ago
That's what the link I gave explains.
- pfdietz 6y ago
  Thanks.