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> 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 i

by twic 2y 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 2y ago
Aneutronic fusion has been previously mentioned, specifically HB11. https://en.m.wikipedia.org/wiki/Aneutronic_fusion https://en.m.wikipedia.org/wiki/Aneutronic_fusion
- willis936 2y ago
  It requires much higher temperatures, and thus suffers much higher Bremsstrahlung. You can sniff out BS quickly with anyone claiming a steady state aneutronic reactor. A working aneutronic design would necessarily be pulsed. Not that it can't be done, but you'd first need to pass through DT and DD performance metrics and then go another order of magnitude. No one's done that yet.
pfdietz 2y 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.
wbl 2y ago
We need a liquid with high heat capacity, large hydrogen content (for high neutron interaction rate) and a solid 300 year engineering history in heat engine applications. Better if it is nontoxic and environmentally friendly as well.
- WJW 2y ago
  But what if you breathe it in!!!1! Dihydrogen monoxide is no joke, many people are killed by it every year.
jmyeet 2y ago
You're talking about the same thing. High energy neutrons leave the system. They cause damage to the container (ie neutron embrittlement) and that's a separate problem. But the real problem is the energy loss from the system. Charged particles can be contained. Personally I think there are limits to even that because a high-temperature plasma is turbulent [1]. Containing that is just a hugely difficult problem. I'm not convinced that nuclear fusion will ever be commercially viable. All while we already have emission-free, reliable and cheap energy production in the form of solar power. [1]: https://www.psfc.mit.edu/research/topics/plasma-turbulence https://www.psfc.mit.edu/research/topics/plasma-turbulence

by twic 2y ago

chasil 2y ago

Aneutronic fusion has been previously mentioned, specifically HB11. https://en.m.wikipedia.org/wiki/Aneutronic_fusion https://en.m.wikipedia.org/wiki/Aneutronic_fusion

willis936 2y ago
It requires much higher temperatures, and thus suffers much higher Bremsstrahlung. You can sniff out BS quickly with anyone claiming a steady state aneutronic reactor. A working aneutronic design would necessarily be pulsed. Not that it can't be done, but you'd first need to pass through DT and DD performance metrics and then go another order of magnitude. No one's done that yet.

pfdietz 2y 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.

wbl 2y ago

We need a liquid with high heat capacity, large hydrogen content (for high neutron interaction rate) and a solid 300 year engineering history in heat engine applications. Better if it is nontoxic and environmentally friendly as well.

WJW 2y ago
But what if you breathe it in!!!1! Dihydrogen monoxide is no joke, many people are killed by it every year.

jmyeet 2y ago

You're talking about the same thing. High energy neutrons leave the system. They cause damage to the container (ie neutron embrittlement) and that's a separate problem. But the real problem is the energy loss from the system. Charged particles can be contained. Personally I think there are limits to even that because a high-temperature plasma is turbulent [1]. Containing that is just a hugely difficult problem. I'm not convinced that nuclear fusion will ever be commercially viable. All while we already have emission-free, reliable and cheap energy production in the form of solar power. [1]: https://www.psfc.mit.edu/research/topics/plasma-turbulence https://www.psfc.mit.edu/research/topics/plasma-turbulence