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“Nuclear fusion is 30 years away; and always will be." I wonder how this phrase manages to hold after 50 years since its inception. We could compare it to the

“Nuclear fusion is 30 years away; and always will be." I wonder how this phrase manages to hold after 50 years since its inception. We could compare it to the state of general AI, but at least in the machine learning field, progress is being made without knowing the feasibility or path to reaching general in AI. In fusion it appears that the theory has already been set and maintaining the chain reaction going for long enough is the limitation (progress being made here), would it be the same case that the final steps are still missing without a clear path, or would the current progress be enough to eventually reach it?

jl6 4y ago
AI research has made slow scientific progress but great engineering progress. Fusion has made great scientific progress but still has a lot of engineering left to do.
- JumpCrisscross 4y ago
  > has made great scientific progress but still has a lot of engineering left to do It’s made serious engineering progress too.
  - ncmncm 4y ago
    Engineering work halted 30+ years ago. There has been no recent work on structural materials that could withstand the neutron bombardment, and no work on extracting bred tritium at parts per billion concentration from thousands of tons of "blanket" material needed for the next day's operation. There is no possibility of any present scheme operating at even 10x the cost of fission. Fission is not today competitive, and falls further behind each day.
    - fallingknife 4y ago
      You can get around the tritium problem with boron-proton fusion. Also gets around the inefficiency of converting to heat / turbines. Obviously not any closer to production (and probably further) than tritium fusion, though. https://hb11.energy/how-it-works/ https://hb11.energy/how-it-works/
      - ncmncm 4y ago
        There is no reason to expect that p-11B fusion is possible. It might be, in a hundred years, if our present understanding is wrong, and somebody figures out how to reflect gamma rays.
        fallingknife 4y ago
        It's been done by firing lasers at a HB pellet, so I assume you mean not possible to be done commercially? And why would you have to reflect gamma rays?
        ncmncm 4y ago
        Obviously you can fuse about anything by accelerating nuclei at each other fast enough. If it takes more energy to do it than you can get back, it is of purely academic interest. Firing lasers comes up many orders of magnitude short. Another alternative is magnetic confinement, but radiative loss goes up with the 4th power of temperature, so would be 10000 times as much as for a D-T plasma, IIUC.
        pfdietz 4y ago
        Are you talking about the company H11B? Their scheme has been soundly criticized in the literature as not working by a factor of ~100.
    - JumpCrisscross 4y ago
      > Engineering work halted 30+ years ago. There has been no recent work on structural materials that could withstand the neutron bombardment We've made massive strides compacting designs, thereby transforming their unit-economic envelope, using low-temperature superconducting magnets. Those magnets continue to improve, driving potential gains in designs faster than experiments can be funded and built. Optimizing for structural materials, or even blanket versus replaceable structure, seems premature when we don't know the parameters or even type of bombardment we'd be working with.
      - ncmncm 4y ago
        Bombardment is with hot neutrons. Period.
Trouble_007 4y ago
Timeline of Nuclear Fusion : https://en.m.wikipedia.org/wiki/Timeline_of_nuclear_fusion https://en.m.wikipedia.org/wiki/Timeline_of_nuclear_fusion
Apocryphon 4y ago
This chart rests upon faulty assumptions about the efficacy of tokamaks, but it does demonstrate how little interest the U.S. federal government has had towards research of fusion. http://i.imgur.com/sjH5r.jpg http://i.imgur.com/sjH5r.jpg https://hardware.slashdot.org/story/12/04/11/0435231/mit-fusion-researchers-answer-your-questions https://hardware.slashdot.org/story/12/04/11/0435231/mit-fus...

jl6 4y ago

AI research has made slow scientific progress but great engineering progress. Fusion has made great scientific progress but still has a lot of engineering left to do.

JumpCrisscross 4y ago
> has made great scientific progress but still has a lot of engineering left to do It’s made serious engineering progress too.
- ncmncm 4y ago
  Engineering work halted 30+ years ago. There has been no recent work on structural materials that could withstand the neutron bombardment, and no work on extracting bred tritium at parts per billion concentration from thousands of tons of "blanket" material needed for the next day's operation. There is no possibility of any present scheme operating at even 10x the cost of fission. Fission is not today competitive, and falls further behind each day.
  - fallingknife 4y ago
    You can get around the tritium problem with boron-proton fusion. Also gets around the inefficiency of converting to heat / turbines. Obviously not any closer to production (and probably further) than tritium fusion, though. https://hb11.energy/how-it-works/ https://hb11.energy/how-it-works/
    - ncmncm 4y ago
      There is no reason to expect that p-11B fusion is possible. It might be, in a hundred years, if our present understanding is wrong, and somebody figures out how to reflect gamma rays.
      - fallingknife 4y ago
        It's been done by firing lasers at a HB pellet, so I assume you mean not possible to be done commercially? And why would you have to reflect gamma rays?
        ncmncm 4y ago
        Obviously you can fuse about anything by accelerating nuclei at each other fast enough. If it takes more energy to do it than you can get back, it is of purely academic interest. Firing lasers comes up many orders of magnitude short. Another alternative is magnetic confinement, but radiative loss goes up with the 4th power of temperature, so would be 10000 times as much as for a D-T plasma, IIUC.
        pfdietz 4y ago
        Are you talking about the company H11B? Their scheme has been soundly criticized in the literature as not working by a factor of ~100.
  - JumpCrisscross 4y ago
    > Engineering work halted 30+ years ago. There has been no recent work on structural materials that could withstand the neutron bombardment We've made massive strides compacting designs, thereby transforming their unit-economic envelope, using low-temperature superconducting magnets. Those magnets continue to improve, driving potential gains in designs faster than experiments can be funded and built. Optimizing for structural materials, or even blanket versus replaceable structure, seems premature when we don't know the parameters or even type of bombardment we'd be working with.
    - ncmncm 4y ago
      Bombardment is with hot neutrons. Period.

Trouble_007 4y ago

Timeline of Nuclear Fusion : https://en.m.wikipedia.org/wiki/Timeline_of_nuclear_fusion https://en.m.wikipedia.org/wiki/Timeline_of_nuclear_fusion

Apocryphon 4y ago

This chart rests upon faulty assumptions about the efficacy of tokamaks, but it does demonstrate how little interest the U.S. federal government has had towards research of fusion. http://i.imgur.com/sjH5r.jpg http://i.imgur.com/sjH5r.jpg https://hardware.slashdot.org/story/12/04/11/0435231/mit-fusion-researchers-answer-your-questions https://hardware.slashdot.org/story/12/04/11/0435231/mit-fus...